Yesterday I tried to upgrade my VM from 25.05 to 25.11. After updating the flake, I ran nixos-rebuild boot but it never finished, because of errors like these:
warning: error: unable to download 'https://cache.nixos.org/nar/0igfq8gmdaarnwjaaj3j7dwqpbykqjfpbfavq3df6qimy93dfsg3.nar.xz': HTTP error 200 (curl error: Timeout was reached); retrying from offset 65536 in 278 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1v1dd9h1kssk0f0ipfffrgdn5hcihdvcjq7fp5lrl1mmcp33w3fb.nar.xz': HTTP error 200 (curl error: Timeout was reached); retrying from offset 65536 in 291 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0z0y81apnibc6bh6512inp4v2w58ybbgjdmk21b3f4pbd64g81hj.nar.xz': HTTP error 200 (curl error: Timeout was reached); retrying from offset 65536 in 317 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1za60lrafswf2q22v8qlb78lpyn43ilf3nv0lj2asd8gzhrvxx1x.nar.xz': HTTP error 200 (curl error: Timeout was reached); retrying from offset 65536 in 326 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0igfq8gmdaarnwjaaj3j7dwqpbykqjfpbfavq3df6qimy93dfsg3.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 639 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1v1dd9h1kssk0f0ipfffrgdn5hcihdvcjq7fp5lrl1mmcp33w3fb.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 540 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0z0y81apnibc6bh6512inp4v2w58ybbgjdmk21b3f4pbd64g81hj.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 516 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1rwfrxx7a7xrqfpdcqhdgnwh60ykpsn58i7dy9k9kqxxhc0bmq0q.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying in 344 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1za60lrafswf2q22v8qlb78lpyn43ilf3nv0lj2asd8gzhrvxx1x.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 639 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0igfq8gmdaarnwjaaj3j7dwqpbykqjfpbfavq3df6qimy93dfsg3.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 1373 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1v1dd9h1kssk0f0ipfffrgdn5hcihdvcjq7fp5lrl1mmcp33w3fb.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 1026 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0z0y81apnibc6bh6512inp4v2w58ybbgjdmk21b3f4pbd64g81hj.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying from offset 65536 in 1302 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1dlsbg15al3bb236gl4zfixcgqqp7qs6ikba8mim4fs693h3wyrz.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying in 257 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1rwfrxx7a7xrqfpdcqhdgnwh60ykpsn58i7dy9k9kqxxhc0bmq0q.nar.xz': Timeout was reached (28) Operation too slow. Less than 1 bytes/sec transferred the last 300 seconds; retrying in 646 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1za60lrafswf2q22v8qlb78lpyn43ilf3nv0lj2asd8gzhrvxx1x.nar.xz': Failed sending data to the peer (55) Send failure: Broken pipe; retrying from offset 65536 in 1127 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0igfq8gmdaarnwjaaj3j7dwqpbykqjfpbfavq3df6qimy93dfsg3.nar.xz': Failed sending data to the peer (55) Send failure: Broken pipe; retrying from offset 65536 in 2106 ms
warning: error: unable to download 'https://cache.nixos.org/nar/1v1dd9h1kssk0f0ipfffrgdn5hcihdvcjq7fp5lrl1mmcp33w3fb.nar.xz': Failed sending data to the peer (55) Send failure: Broken pipe; retrying from offset 65536 in 2132 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0z0y81apnibc6bh6512inp4v2w58ybbgjdmk21b3f4pbd64g81hj.nar.xz': Failed sending data to the peer (55) Send failure: Broken pipe; retrying from offset 65536 in 2263 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0bwwlg2k6fh5ba62yhhjxpgpif4qivb5jfxdrar9ywwjxrcafj7h.nar.xz': Failed sending data to the peer (55) Send failure: Broken pipe; retrying in 287 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0xgyabmdahw0174q8zalfc3sxz7n8q5674jz0a46l1wgknkx5sd6.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 77364395 in 293 ms
warning: error: unable to download 'https://cache.nixos.org/nar/136jg63hzanqrcvzzry1bd8dgsl2k7wcghvfxj00ksdg9i51wq30.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 63762840 in 321 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0aiyi4d807mg7mz4sd78z576ysp0vvww2d288xmzpbiz87r6ik9k.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 57663068 in 322 ms
warning: error: unable to download 'https://cache.nixos.org/nar/08kyy1qr8n0ri0rg548m3hk1h9pzrd1vl74qnjviik0g627rdrh3.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 52802732 in 283 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0lnrpzklbmv2cmrg7vvsd7rblr147pvjb75vf8dya634ig6jdc3s.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 41645418 in 274 ms
warning: error: unable to download 'https://cache.nixos.org/nar/01k7mdlrf7kcwfy0kj86s0lhbzz6xib4v4dp99ff64jyc8y4r1va.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 20276507 in 265 ms
warning: error: unable to download 'https://cache.nixos.org/nar/0gv05lydlpsw3z0j7dvq61mxfr869rg6b5kf76vmckqww81w9baa.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 17317888 in 277 ms
warning: error: unable to download 'https://cache.nixos.org/nar/076ll1k4djlbs9pljz57m3amga040ikxcv53gr97nyz1brg1b3n2.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 5636096 in 346 ms
warning: error: unable to download 'https://cache.nixos.org/nar/15pg9m1af2bi63l27kn288z8cxvnqnqrlgkhqhrsb6j9jcaipxz1.nar.xz': HTTP error 200 (curl error: Failed sending data to the peer); retrying from offset 4583009 in 299 ms
[4/479/650 built, 16/2129/2206 copied (11436.5/15491.9 MiB), 2147.3/3704.6 MiB DL] fetching gnome-text-editor-49.0 from https://cache.nixos.org
A few seconds after I copied the output above, the gnome-text-editor download also failed with with the Timeout was reached (28) error. I aborted the rebuild after about 2h.
Before the download errors started, I noticed that it had to compile some vim plugins (e.g. CoC, afair), which I found a bit surprising, but it could be pure coincidence.
Any idea what went wrong and how I can fix it? The VM has a 100GB disk (52GB unused) and 4 GB RAM.