This is all more than vague...
First of all, the account does not seem to be blocked right now? All we have is a statement of that person (of whom we know little to nothing?)
On the gitlab page the author wrote:
This move is because gitlab.com once suddenly blocked our account and another time made the repository private without any prior notice,
"ONCE" => as in "one time in the past". (One times is still one time to much, but...)
And they had issues before (moved to private).
Other than the statement, there is no proof. The user may have done so himself by accident, or given to much access to a contributor, or have been hacked..... I don't say any of this was the case, but I for once have no objective information about what really happened. (And any extremely vague hint by someone else, alluding of that person self-claimed non-proven inside knowledge... well that does not help either)
Another easy explanation could be, he logged in from another browser => then you get an email, if that was you, or if you need to change your password. It contains a link, to be clicked only if it wasn't you. Maybe that got mistaken?
Or maybe there once was a fault/bug/mistake at/by GitLab? Happens to the best. But if so, it doesn't look like it's something that is out of control. It's not like everytime you read about gitlab it ends in a warning....
All I can say is
- he got access again, because he posted that statement.
- the repo is still there, accessible to everyone
All the rest seems speculation (as are all of my above possibilities)
So overall, I don't think that having a project at gitlab is a risk of loosing access.
Speculating again they (as a big entity) a probably in a much better position to protect my data for me against loss by hardware fault, hacker attack, even my own fault. A better position than I would be in if I hosted myself, or than a smaller entity might be.
And as for trust, in the grand picture there is no reason not to.
Also git is distributed. We always have a copy. Only the issues and merge requests, we don't have outside of gitlab.