Is it literally [Action] [Action] or there's some action behind that?
Can you check files at .local/share/rockpoold/<mac>/timeline/<uuid> and try to figure out which of them came as empty? Eg. filter out those which came normally and remaining with alarm bell icon would have system://images/NOTIFICATION_GENERIC as an icon.

Also there was a bug where UTF strings are improperly trimmed to fit content limitation and when they overflow you'd get empty message. Clear indication of such message would be body field more than 512 characters and with at least one non-ASCII character (umlaut, háček/čárka, кирилица, €/£, etc). After UTF8 expansion resulting byte sequence will be longer than 512 bytes and would cause overflow. It's fixed in git but last beta doesn't have that fix yet.