Conflict with event tickets plugin

There is a conflict with event tickets plugin.
Any adress with a language slug page becomes 404 (even homepage)
How to reproduce this error:

1. install&activate sublanguage and event tickets
2. add a secondary language to sublanguage
3. (Show language slug for main language in site url) or (try to access any page in the secondary language)
sometimes it works ok briefly but refreshing/opening another page shows 404.

deactivating event tickets doesn’t help – you need to change theme back and forth for the site to become live again (deactivation routine of some plugins such as gravity forms also helps to bring the site back to life)

it happens also on a fresh wordpress install

Probably it’s event tickets plus developers fault (their recent update to event ticket plus made the entire site crash – even wp-admin became unaccessible)

I’m trying to install sublanguage on a site with 40+ plugins, this is the only conflict so far