Looks like a bug I was able to reproduce this is NPM 12.2 and SAM 6.6 as well as with NPM 12.3 and SAM 6.6.1
This has bit me hard several times, bug has been around for years. NEVER hit "Select All" anywhere in SolarWinds, cannot be trusted. I once unmanaged EVERY SINGLE APPLICATION (all 12,900 of them) in the environment this very same way. Couple that with having no ability to sort applications by status, took me a good 4 hours to recover from that.