Thanks for your detailed explanation.
I played around with the sync settings a moment ago, but I it feels like it’s down to total luck
whether the setting changes actually do something which is really irritating.
For example just now the OSSC only managed to sync when I set the Analog sync Vth to 56mV (everything als resulted in permanent no sync), but even then it dropped out every 30 seconds or so and a restart of the console often lead to a total sync loss no matter the setting.
Even if I manage to get it synced it never lasts long and the same settings suddenly don’t work anymore.