TCL error: _cgc_pick_clientside

I found this page searching for an answer to the exact question  was asking, kept searching, and was eventually able to find this Support Solution:

https://support.f5.com/csp/article/K54469707

It mentions that this is actually a big3d error and sure enough, when I checked /var/log/gtm I found SSL Error messages that matched up with these /var/log/ltm messages. Even better, the /var/log/gtm messages list the IP that these connections are coming from, which in my case turned out to be one of our internal security appliances doing a scan.