R4XX UDP send limit

I have a R412M AFF with firmware M0.10.00 [Mar 28 2019 17:13:41].
I discovered I can only send 20 packages. Then packet 21 and so forth I either get no response from the modem (within the 3 minute timeout) or I get:
+CME ERROR: Operation not allowed

I also have a R412M AFF with firmware M0.09.00 [Jan 31 2019 18:59:31].
I do not have this problem there.

I tried multiple times, and the limit is always exactly 20.

The code that I use:


I’m sending the packets with 30 seconds intervals. DRX is disabled.