VirtualBox 5.1.20 had a lot of regressions:
This is a maintenance release. The following items were fixed and/or added:
VMM: fixed VERR_IEM_INSTR_NOT_IMPLEMENTED Guru Meditation under certain conditions (5.1 regression; mostly Mac OS X hosts; bugs #15693, #15801, #16274, #16569, #16663)
VMM: fixed software virtualization on Solaris hosts (5.1.20 regression)
Storage: fixed a potential hang under rare circumstances (bug #16677)
Storage: fixed a potential crash under rare circumstances (asynchronous I/O disabled or during maintenance file operations like merging snapshots)
Linux hosts: make the ALSA backend work again as well as loading the GL libraries on certain hosts (5.1.20 regression; bugs #16667, #16693)
Linux Additions: fixed mount.vboxsf symlink problem (5.1.20 regression; bug #16670)
Is .22 in the pipline?
Released friday the 28th... so on my main machine i stay on .18.
Have a nice "Tag der Arbeit"!