I have the same problem on macOS 10.14. Not so bad because I can just start NX manually, but still.
Did the archive the logs command you suggested, but:
crispin$ tar -czf nxclient-logs.tar.gz ~/.nx/M-*
tar: /Users/denning/.nx/M-*: Cannot stat: No such file or directory
also …
crispin$ ls .nx
./
../
F-M-crispin.hsd1.co.comcast.net-13002-22C8D24806C865257C0D2473A8936D5B/
K-localhost-370-9FCF08C0A3777842F70B111BE7DDEB3C/
K-localhost-869-04280961C1306EDDC0F8AB9BFCCE6DF2/
R-localhost-25552-987C1A3AED21CED8546A2E270051C546/
R-localhost-732-47D13B382084BDABDEBD356814400CD4/
cache/
config/
temp/