I could sorta see a situation where the reality is "we're in the middle of a miserable transition and it'll clean up when we're done" but I don't think anyone has confidence that's all it is at this point.
Even that doesn’t really make sense to me, unless they’ve done it in a way where everything has to move at once.
Everywhere I’ve worked, if a migration is causing this much downtime then you kill the migration or slow it down. If every change has a 10% chance of bringing the site down, you only do a change every week or two until you can work out the kinks.
Reminds me of the bank for my business where a larger bank with terrible IT bought a smaller bank with great IT - guess which systems they standardized on? Online banking is still much worse than before and the web interface still says "will be migrated by end of 2023" for some parts. Many customers just left and complaints were widely reported in the media. I probably should leave, too.