This feels like telling your Granny how to suck eggs.

What position have you the rear bag and front rest in? Your rifle has a heavy barrel and while probably not as heavy as others a heavy barreled rifle will want to "tip forward". I had this with my BR rifle but she was over 13lbs. IOW as heavy as my FTR rifle.

If I had the front rest to far back (towards the trigger) the "tipping point" of the rifle would be moved and unless I kept identical cheek pressure (which is very hard to do) on the stock she would give me vertical strings. Now I shot mine free recoil so this amplified the effect.

My solution was to have the front rest as far forward (towards the muzzle) as I could and the rear back in the "sweet spot" to make sure the rifle was completely anchored. IOW its centre of mass was between both rests and not favouring forward or rear "tipping".

Another tip is to make sure the butt stock is well placed in the rear bag. Don't just "rest" it into the rear bag which will allow for movement. I used to tap mine down into the bag to get the best, snug, fit I could. Something I picked up from the F-Class lads (F-Open).

Lastly have the rear bag properly filled. Leave no room from manipulation and try stop yourself from squeezing the rear bag. You won't keep the same pressure on it during each shot or even at the moment of firing and this will cause variations in the string.

As said at the start this feels like telling someone what they already know, but I can't count the amount of times I've forgotten something I knew.