Yes I saw your original post, but didn't answer, cause I don't know. Personally haven't noticed this problem, which doesn't mean it's not there. I usually don't run championships, but single races, as each day there are at least 3 cars that I want to race that day.
For the GTO, use the bop from this post, which uses updated cars from the time that was posted originally:
https://www.gtplanet.net/forum/thre...ral-discussion.307899/page-1132#post-13099177
I also did a bop for btcc 2018 and 2019,if you search this thread. Not at a computer right now, so not 100% sure, but if I remember correctly I think you need to lower the Astra restrictor to 3 (the car was later updated by emkay), and raise alfa to 8 in 2018 season. And for 2019 I made updates to both bmw, subaru and Honda. Links don't work anymore, can send you new links in pm when I get to my computer if you want. There is also a few other I did as well, if you search the thread (btcc 1991,1999, itc 1996,...).
For BOPs from other users I don't know.