Bitcoin Core Multi-wallet limit to 333 wallets
Ok, I found a solution. Adding 

set_lk_max_lockers 400000


Did the trick.  

https://docs.oracle.com/cd/E17276_01/html/api_reference/C/set_lk_max_lockers_parameter.html

I tested and was able to auto-create and load 932 wallets, until I hit an out of memory error:

Logging region out of memory; you may need to increase its size
DB_TXN-&gt;abort: log undo failed for LSN: 227 171878: Not enough space
PANIC: Not enough space
PANIC: DB_RUNRECOVERY: Fatal error, run database recovery
PANIC: fatal region error detected; run recovery


Setting: 

set_lg_regionmax 1048576


Resolves the above Logging region out of memory; you may need to increase its size issue.