Why are some claimants receiving E50 form when transferring from ESA to UC?

First of all, thanks for reading this, and any consideration you might be able to give this?
Why are some claimants receiving the E50 form to fill in, after applying for UC during ESA transfer?
I am guessing at this point that these forms are not all being issued in error?

Is it the case, as the moderator posted, that ESA (now UC) is not awarded indefinitely, and some cases will be coming up for review shortly anyway as the DWP works through the backlog, and these just happened to coincide with the transfer process?

Obviously nothing can be done about this.

Or is there some other detail that a claimant might enter on their online application that might trigger a review - for example, minor change of wording describing their medical condition, so what the claimant writes online is not exactly the same as what the DWP already have on file?

I am in the support group preparing to transfer, and the paranoia is making me second-guess things which might be straightforward.

Thanks for any help,

Droopy