This problem isn't fixed on latest patch yet?
Although, this is a rare bug that one may encounter. I'm afraid you have to re-import everything else.
But yeah, the new patches of editors are prone to this risk. I even encounter this in 1.30+ sometimes.
(Luckily, restarting my editor that time shows up the correct file sizes again so I think it's just a glitch)
With that being said, it's very important to have backups when working on something big data you're
afraid to lose in this kind of situation one may never expect to happen in the first place. Just a warning.