BIG problem.. locked in gear!

My cars snycros are bad very bad… it doesnt go into 3rd gear AT all after 3k rpm and same w/ 4th.

So i drive the car knowing that. But now i was driving down the road went to down shift coming off the highway and it wouldnt let me into any gear at all, from neatrul it let me out of gear no problems

The whole thing locked up once i took it into neatraul from 5th to put back into a lower gear… then i came to stop turned it off then on tryed to get it in gear no luck. it lets me shift threw gears when its turned off tho…

then i put it in gear and turned it on and it was fine except for the snycro problems. I took it to a shop to look at the clutch and cable both are perfect they said.

so my question is why is it locking up like that its happened 3 times and i had to turn it off put in 1st gear and then go

can that be the syncros causing that problem???