I resolved this issue. From: https://github.com/roots/trellis/pull/1341
Changes the default vagrant_ip from 192.168.50.5 to 192.168.56.5 (note the subtle change from 50 → 56).
A recent change in VirtualBox means that only IP addresses in the 192.168.56.0/21 range are allowed.
Vagrant is now validating that the IP is within this range as well (hashicorp/vagrant#12564).