No more issue at all here i.e. Arch Linux with package 0ad-0.28.0-2 (reverting to js115 from js128) as @ffm2 wrote yesterday evening (just not specifying the version).
ty @Stan` for clarifying the spidermonkey bug that caused the issue.
Now back to my issue as I'm lagging behind the game's new speed (efficiency) even on a light setup
As soon as a release candidate gets published, mod authors should take care to update their mods. From this point on breaking changes are unlikely and a release candidate is a clear sign that a release is about to come out soon.