For me the issue is fully repeatable. Sim is updated to SU13 (no issues). Couatl starts automatically (as usual) and is seen in the systray - in sim GSX menu just spins and does not load. I exit Couatl, wait a bit and then restart it. It again appears on the systray, however at this point when GSX menu is selected in the sim, it appears (showing the loading spin) and then immediatly disappears. very strange. SU13, GSX 2.7.6, FSUIPC 7.3.21
I'll keep trying.