Actually, the number of CVT issues has declined tremendously - there's very few 2021's that have had issues, and yours is an outlier.
As for your issue, it most definitely could be caused by an electrical issue. That TSB helps diagnose what is broken, but doesn't rule out electrical issues, valve body issues, etc. New CVTs are generally coming with new harnesses as part of the "CVT kit".
Chain slip is caused by a number of factors, including bad sensor, bad harness, TCM malfunction, water in CVT, improperly filled CVT (eg: during service), drained/partially drained CVT (eg: car taken to Jiffy Lube for oil change and they drain the wrong thing), the wrong CVT fluid used (eg: if a shop accidentally drains it, and then fills it with anything other than the Subaru specified fluid).
In all such cases, replacing the CVT fixes the issue, including any of those causes (assuming the TCM passed testing, which would have been caught during TCM relearn if not).
Your old CVT will not be ripped open here to be diagnosed, so, if you're the type who's interested in the "whys" and "whats", you sadly don't and won't know the cause - but I'd bet good money that it's one of the above.