@Mitch13 - have you tried this
Create an empty library (TESTLIB) on another drive (eg the 1TB drive on the ASUS Win 7 box)
Use the Copy to Library feature of Calibre to populate TESTLIB from the existing library on the portable SSD (I'll call it PRODLIB).
Do all you can to reproduce the problem on TESTLIB
If you can't reproduce the problem on TESTLIB then the problem probably lies with the portable SSD drive (ouch) or PRODLIB. I would replace the existing PRODLIB on the SSD drive with TESTLIB, if the problem recurs then it is probably a problem with the SSD drive
If the problem still exists with TESTLIB, then it could a 3rd party app that you run on all three systems 'interfering' with Calibre - try running after a Safe with Networking Boot, or shut down/kill all other non-essential tasks.
I recently replaced my daughters Gmail notifier because it was interfering with her RSS news feed aggregator - she's a journo
BR