“Why wasn't this bug caught in the first place” - this isn’t an attack on whichever developer introduced the bug.
It’s a (totally fair) attack on Signal’s lack of QA/testing in their development + release cycle.
Do they implement peer reviews on PR? Multiple reviews on changes touching mission critical code (ie. data migrations)? Do their test suites provide adequate test coverage? Do they have a manual Q/A process that involves real people testing new releases?
Considering Signal’s funding, I would hope the answer to all of those questions is yes.
But if it’s possible to release code that completely corrupts the app with no known fix, I suspect their test coverage and Q/A processes aren’t as robust as they need to be.