After 2021.4.12 on my S I have an odd charging behaviour.
At home I keep it plugged into the HVWC and the SOC set to 70%. After the update there is the usual clanking of contactors and fan whirring about every three or four minutes, the car charges for a minute or so then stops until the next charge starts in three or four minutes.
I'm wondering if something's changed in the bug fix update which makes it keep at exactly the set charge state. I would expect that the program would allow the SOC to slip a little below that set before charging up to slightly over to avoid almost constant reconnection.
You might want to confirm one thing. Do you have charging set to start at a specific time or the be charged by a set time for departure? In my case I do not have any of that turned on. It will start charging whenever I plug in and the SOC is below my set point. I used setting to start charging at a specific time for several years, but turned all that off several months ago when I started to get signs my MCU1 might be getting flaky (didn't want to get caught with a failed MCU and unable to charge at home).
I started noticing last year the behavior you describe where as soon as the SOC drops below the setpoint, so 1 percent SOC loss, it automatically starts charging again. I forget what release that was, but well before 2021.4.12. Previously it wouldn't trigger to start again unless it fell about 3 percent or so below the limit.
Personally, I don't care for the new behavior. This is one of the reasons that I've now gone to not charging every day, but manually control when I change by keeping the setpoint at 50%, then when I want to charge to say 70% - 90%, I manually raise the limit up, let the car charge, and soon as it finishes, reset back to 50%.
I know vampire drain increased significantly as a result of some of the changes/feature the past couple years which keep the car on more of the time (sentry, summon on demand, climate overheat protection, etc). I don't know if this change somehow is a way to mask vampire drain/loss when people are plugged in at home? Or counter all the people that I've seen complain that I had my car set to charge to 90%, but when I went to leave is was at 87-88% and complaining as if something went wrong and it wasn't charging to the correct value. Either way, I'm not a big fan of it personally, but I know how to manage it in a way that it doesn't impact me any more.