Unable to hot-plug USB devices

I am unable to hot-plug USB devices with my laptop (Thinkpad E495). They only work if they have been connected at boot, reconnecting breaks things again. They do not show up in lsusb. Connecting devices does show dmesg errors:

[  373.889901] xhci_hcd 0000:05:00.3: Error while assigning device slot ID
[  373.889911] xhci_hcd 0000:05:00.3: Max number of devices this xHCI host supports is 64.
[  373.889919] usb usb1-port4: couldn't allocate usb_device

What can cause something like this?