You’d like to think professional chimney cleaners would know all about this kind of thing but maybe yours is new to the job so here’s my suggestion.
A wood stove built in the 1990’s is not really that old. Of course, we don’t know who designed it so it might be different to what I envisage but let’s try this for starters.
Take a look at the inside of your stove when it is cold. Does it have firebricks up the side? Does it Block a bit like pavers? If it does, push against the baffle (the plate above your firebox) to raise it just a little.
Then, remove the top layer of firebricks. It’s a dirty job so be prepared for it. Spread newspaper around and have your dustpan, bucket, etc. ready. Of course, you need to empty any dust and debris from the bottom before you begin.
I expect the firebricks are holding up the baffle. Once you’ve removed the top layer, you’ll know if the baffle drops without resistance. If there’s creosote on top, you’ll have even more mess so be ready. Keep control of the baffle. Lower it gently. You’ll soon figure out if you need to remove more firebricks or not.
Firebricks should just slot back in without difficulty when you’ve finished.
If you can raise the baffle at all, even just a tiny bit when you push it upwards, I suggest this is your solution.