Internet disconnect during lease renewal while running multicast TV stream

The router is working fine if I don't use multicast TV, otherwise internet get's disconnected on every lease renewal for a minute (which is not funny at all since my ISP has 30 min lease).

I have the following setup:

OTO socket -> fiber cable -> SFP -> media converter (TP-Link MC220L) -> cable -> Router (XR500) -> cable -> PC

After problems described above and some debugging, I have decided to factory reset router, make this setup and just test this. I did the router default setup, firmware is up to date (V2.3.2.40) and I have unchecked "Disable IGMP Proxying" in WAN settings according to my ISP instructions (https://www.init7.net/en/support/faq/TV7-Voraussetzungen/). Then I used VLC player on my PC to start network stream with the TV playlist from my ISP (https://www.init7.net/en/support/faq/TV-andere-Geraete/). On every lease renewal (so every 15 min) the stream freezes and internet get's disconnected for few minutes. The lease renewal is also logged in the router with the following entry: "[Internet connected] IP address: XXX.XXX.XXX.XXX, Date & Time". This entry occurs every 15 min in the log. To confirm this issue, I also did this manually: by pressing "renew" button in the "settings -> monitoring -> connection status", TV stream freezes and internet drops.

I have also removed the router from the chain, so directly connected my PC to media converter and then VLC TV stream works without interruption for hours.

Also when I don't have TV multicast stream running, lease renewal does not create any problems, I can watch Netflix and play online PS4 game without interruption (lease renewal occurs every 15 min with internet connected log entry there as well).