To follow-up...
Reverting to Vortex 1.0 did not resolve things. I reinstalled 1.2.
Since I had been using this microsd with my T6 (with 15000 limit), I had previously staggered my music library so I could transfer just under 15000 songs (to be scanned by hiby), then would transfer the rest onto the card (to be scanned by Rockbox). This gave me greater control of the hiby database contents.
So, I formatted my card using the x3ii, then transferred 14994 songs onto the card.
Strangely, when hiby scanned, it completed, but listed 15039 songs found from the scan.
When I initialized the Rockbox database,15002 songs were found.
The only things on the card are folders and mp3's (used Total commander to purge all other file types).
On my T6, both hiby and Rockbox recognize 14994 songs on the card.
Not sure why this is not the case on x3ii.
The actual full amount of songs that failed to scan previously was 28879.
Assuming the glitch continued, it may have for some reason read above 30000, and perhaps this is why it kept rebooting after the initial scan.
When I get a chance, I'll try to reduce it to 25000, and will see what happens.