AVCS only moves the outer sprocket rotation slightly compared to the camshaft. Even if it’s dead the cam should still spin as freely as the others. And if turning using the cam removal tool or turning from the camshaft bolt the AVCS part is irrelevant.   The AVCS has a position sensor and solenoid so the ecu knows its position if it was lagging or failed. Even then I’m not sure it’d hit a valve if fully out, plus the ecu would have been in limp mode. Any resistance is bad bearings or bend valve etc.     The chance of belt snap for a hard to turn by hand cam seems low. it is possible but unlikely there was oiling issue. That could cause a belt to snap but then the cams are usually rock solid stuck and hand turning them you’d notice then crack like a stuck bolt before they turned more freely.   Much more likely it’s from post belt snap and valve to piston. As @boon said any valve contact should show on the piston. if there is any then no chance it was avcs. Don’t all Gates belts have their logo on them so if it didn’t then it’s was likely a cheap copy.

Unfortunately that's raw ChatGPT from a spam bot and probably has nil value

Yes good thoughts there, it's only one cam that's hard to turn. I can I identify a faulty AVCS sprocket? And maybe the belt was new but the tensioner wasn't!   Many thanks for your opinion 

As i mentioned in another post I've been cleaning and blasting parts so they dont have the labels on them anymore. Can anyone tell me how to tell which is which side and which end is toward the diff and which is at the hub end? The front lateral arms have a hole thru them and one has an "O" stamped beside the hole while the other has a raised dome. Cheers.

no worries & I have shared on the "Oldschool Subaru NZ FB Group" too here : https://www.facebook.com/groups/2190477217846737