Not usually, no.
I cant remember it happening… maybe it did some years ago…
Obviously that would be a show-stopping problem.
Yet - manjaro is rolling release and systems continue to run … so that tells you that if there ever was a problem it was recoverable.
Theres really not anything extra to say about grub over any other system-critical package.
If you follow the correct practices/procedures you are highly unlikely to encounter very many problems … if you do then they should be fixable … maybe even by a simple update.
If things like this worry you … then keep backups.
Or … if they really scare you … consider not using a rolling release system at all.
With the only semi-definitive manjaro guide being noted as non-working:
[How To] Convert to systemd-boot
Then your resource is this:
systemd-boot - ArchWiki