My main used to be Bulwark and I hardly ever missed a parry. Then for a week or so I stopped playing the Bulwark and levelled a Tactical,  a Sniper and a Vanguard. Now today I logged back in  as Bulwark and tried to run a few missions and  to my  surprise I am not able to parry anything. 

Even though I am  parrying fine  with other classes but on my Bulwark I can't seem to parry reliably at all even with Fencing weapon. Even though before I used  to parry without any issues even with a 'Balance' weapon.

I have no idea what's going on or why I am no longer able to parry on Bulwark. Has this happened to anyone else or can someone provide some insight why this might be happening? 

Sorry brother but that sounds like a bad case of skill issue. If you are still able to parry perfectly fine on the other classes you may need to take a closer look at your wargear to see if you had, in anticipation of the block changes, swapped weapon or two over to block then forgot to change back.

Yea I am parrying fine with other classes (even  with 'balance' sword) but with Bulwark I am using  'fencing' power sword and still can't parry reliably at  all. It seems like  that Bulwark's parry timing is a bit different than other classes. I don't have any numbers but it certainly seems so, i dont know if 'block' mechanic has something to do with it.

I always had an issue with bulwark because parry button and shield block are same. So only on bulwark, I always double click to parry, an old trick I read somewhere on these forums months ago. But if you’re doing same as always, must be the slight changes and reversions of changes in 5.0 and 5.1. Unfortunately, you might need to relearn the muscle memory based on slight timing changes.