Transitional protection erosion due to DWP ineptness?

Hi,

I helped a friend of mine transition to UC from ESA when his letter arrived, using the excellent guides on this web site of course.
I learned a lot, and particularly noted the warning that the DWP have been known to erode the transitional protection due to their own mistakes, rather than the stated reasons it should erode.

My friends TP has been reduced from £223.33 in May last year, to £159.99 this month.

Most of the issues has been that, unbeknownst to anyone, other than the DWP, he was receiving both types of ESA. In migrating him, the DWP gave him full UC, then realised their mistake and started to faff about with his payments. Some months he has received just over £1,000 UC as if he had no new style ESA, and some months he has received just over £300 from UC.

They love tinkering with his payments. For example, his May 2025 payment was revised both at the end of May and also in August 2025. It has been confusing to say the least.

Now that I have gone on too long, my question is, where can I find more information on transitional protection and is it likely I can help him to regain some of the £223.33 he used to get? All input greatfully received, with my thanks.
Em.