severe bowing of tri-x

I was given some old expired tri-x from a local camera store. A client brought in a shoebox of old exposed film and a couple of rolls of unexposed tri-x and ektachrome were found in there and sorted out. I was the happy recipient of these. So I shot the tri-x and developed it and noted when it came out of my processor that it behaved much differently than tri-x normally does for me. First of all, the film was stiff- perfectly straight and had very little bend in it. There was also a severe bow to the film across it's width (which is why it wouldn't bend or curl). Once I "popped" the film trying to roll it the entire roll curled up almost instantly on it's own. Cutting the negatives for scanning the bowing was even more pronounced so that it barely fit in my film holder- sprockets were visible on either side of the holder and required tape to keep it in the mount. I was able to stretch them and they scanned alright-ish. I've only shot one other roll of expired film in my life- is this a normal occurrence?

My most problematic film was old slides stored in rolls after developing. But if you put any film between book pages and wait couple of weeks, it will resolve most of the problems.

I have seen this with old negatives. I've tried re-wetting, soaking, Photo-flo etc. Still had terrible curl. Back in the old, old, times film would be advertised as "non-curling" I suspect that the modern films have come a long way.

I would cut the film in strips, load into PrintFile sheets, stack them up and put a large heavy book on top and leave for several days or weeks. Eventually that will flatten them.

Film will take a "set" if it is left curled on a spool or in a canister/cassette for many, many years.
There are some tricks that manufacturers have used over the years to help minimize the effect, but you can't totally eliminate it.
You should have seen the curl in the 60+ year old film I developed a couple of years ago!

Normal.

Does you negative carrier actually squeeze the two glasses together, or is the top glass laying on with gravity? Some Durst carriers needed little clips to hold the top glass down. Maybe you are missing something from you negative carrier that is not holding it tightly together.