Adobe Reader DC Embedded Index Advanced Search on a Windows 10 VM returns 0 results for some users

If I log in to a physical Win 10 Desktop as domain\testtest (8 character user name), I can perform the search successfully.  

If I log in to Win 10 VM as domain\testtest (8 character user name), I can perform the search successfully.  

If I log in to Win 10 VM as domain\testtest2 (9 character user name), the search fails - returns 0 results.

I'm used the Edit > Advanced Search, using Adobe Acrobat Reader DC 2021.011.20039.  Different users on the same Windows 10 VM get different results.  After testing and troubleshooting, the problem seems to happen with user names of 9 characters or more, and succeeds with user names of 8 characters or less.  That seems crazy and maybe it is, but that's my only lead so far.  I've tried duplicating a domain user with the same memberships and policies, but with different number of characters in user name, and that's what happens. I have also tried 2 registry changes related to embedded index - both HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\(product name)\(version)\FeatureLockDown (bToggleUseEmbeddedIndex DWORD val 1) and even tried HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Adobe\Acrobat Reader\DC\FeatureState (bFallbackOnix32 DWORD val 1).