Have you also done tcpdump on two devices to see that config sync request packet is send by the active device and recieved by the standby checked the iQuery part of the article and used iqdump to verify the iquery communication during sync?
https://support.f5.com/csp/article/K13690
https://support.f5.com/csp/article/K411
https://support.f5.com/csp/article/K13637
Also see this as this is why I proposed full force sync as with big configs the incremental sync may fail because of the limit 1024 :
https://support.f5.com/csp/article/K10762232
https://devcentral.f5.com/s/question/0D51T00006uM4MK/advantange-and-disadvantage-of-full-sync-and-an-incremental-sync
Check the /var/log/ltm logs during the sync operation and you can also add them here and also a screenshot with "advanced" view as your previous screenshot is "Basic"