TVheadend dropouts when backing up via TimeMachine or using SMB


I’ve started to suffer from TVheadend stream dropouts when backing up my computer via SMB configured to be seen as TimeMachine compatible device. SMB is installed in a standalone Debian Buster LXC container. This wasn’t happening earlier (like two months ago) but now is present every time I do backups and is very annoying. My TVheadend client runs on a separate machine on LAN with wired connection. When the network is idle, no dropouts occur. The issue also doesn’t happen with simple SMB copy operation. And it doesn’t happen when running a network SpeedTest (500 MBps network) speed so it probably isn’t network-related but maybe CPU or HDD access? I’ve even tried limiting the container interface traffic with powershaper to some reasonable speed but to no avail. It only happens with TimeMachine backups.

Do you have any pointers what can be causing this? Any sugestions on how to fix this are welcome, thanks!