With downgrade I have to uninstall the version an install the new version.
You can run LS 3.x and LS 4.x in parallel, no problem. But I understand that downgrading is significantly more work, because you CAN NOT transfer data from LS 4 to LS 3.
In anyway, I think currently there is no version of LS 4.x that we can recommend to upgrade to. Of course, you should always be on the newest. But this will not guarantee that the errors are solved. Some will, others won't.
At the moment, I would totally refrain from using LS 4.x for production. There are just too many open bugs that need to be fixed over the next couple of months (but please make bug reports for all problems that you encounter with LS 4.x, only that way LS 4.x will become really stable one day).
So upgrade to the latest LS 4.x available in the download section and see if it resolves the problem.
But, if possible, install LS 3.x in parallel and run the next surveys on that version, until LS 4.x is more stable.