Looking back at my stream you already dropped down the standings in the live timing after completing lap 1 and then properly disconnected a while later during lap 2 - a problem I know all too well having suffered it for many months myself.
In case you wanna test your connection:
Try replicating it by joining an empty server, voting to the race and then completing the first lap in
more than 2min (you can just do a lap at full speed and wait before crossing the timing line, doesn't matter), the longer you wait to finish lap 1 the more likely you are to successfully reproduce the disconnect.
Then continue driving while checking the live track map on the webpage (either having it open on a 2nd monitor or your phone) until your dot stops moving on the webpage, which is when you properly disconnected (I was able to speed this up by sending a chat message after starting lap 2, which would disconnect me instantly).
You can even try to do the same thing with a short first race lap too (I see Server 2 has F1 1988 on some short tracks) and you'll likely never disconnect after completing the opening lap quickly.
Testing aside, this would mean your IPv6 connection doesn't deal well with the old SimBin games and you'd need to switch to IPv4 for racing them - this can be either through a setting of your router or you have to contact your ISP and ask them for a
real IPv4 address (no tunneling, DS-Lite or such things as far as I understand it

).
In my case locally setting my connection to IPv4 was one of the first things I tried, yet the problem persisted until months later I found out my ISP wasn't actually giving me a "real IPv4 address" without specifically asking them for it. After that I've not had issues since so hopefully that same solution is true for you.
Also here's a picture from my troubleshooting process, the correlation between a disconnect after lap 1 or being able to complete the race and the opening lap length being clearly visible.
