not sure if this helps, but i was able to open a couple of 5.5.5 projects with v5.5.2 and 5.5.3. I didn’t get any error messages on opening. On saving it did mention the version discrepancy and hit me with a prompt about saving a ‘new version’, or ‘overwriting’.
note: they were pretty simple projects - not sure if there’s possibly some new functionality in 5.5.5 that I hadn’t employed which might give you an issue if opening in an older version…? (i.e. - attempting to open a 5.5.5 in 5.1 gave an error about some corrupt data).
also: i’m on a mac so not sure if a pc would react differently…?
meant to add: i don’t have 5.4 so couldn’t try that specifically.