No stun requests

Hello.
I need help to debug my problem.

For some reason, asterisk not sending stun requests, and, consequentally, not offering srflx candidates.

Asterisk version: 20.6.0~dfsg+~cs6.13.40431414-2build5 (ubuntu default)

rtp.conf (partially):

stunaddr=stun.l.google.com:19302
ice_deny = 172.16.16.0/20

There are no related error shown in console from asterisk -r, however, there are many errors in /var/log/asterisk/messages.log with text

res_rtp_asterisk.c: PJ ICE Rx error status code: 370400 ‘Bad Request’.

I see no requests to the STUN server in wireshark (but I could miss one, because I am not familiar with the tool).

Could anyone help me with the problem, or at least show a direction to dig more info about the error?