I'm really sorry but it's the first time that I used a ML and for some reason my mail client added quotes to the Subject so this mail wasn't added to the intended thread.
I already sent a new message with the right Subject.

Il giorno mer 20 apr 2022 alle ore 16:15 Simone de Blasiis <simone.deblasiis@teameis.it> ha scritto:

Hello,
we noticed the exact behaviour on Kamailio 5.5.4 and topos.
If we disable topos the UPDATE messages are being recognized as loose in the WITHINDLG route and everything works.
When topos is enabled the UPDATE messages fail the loose_route() check and even if we force the record_route() the message is still not being forwarded.
I had just posted my own thread here because I didn't see this one.
I'll proceed opening an issue on GitHub so we can track this.
Best regards
Simone