My PT sessions were always 2x a week for about 2 weeks then spaced out more as the symptoms resolved...

I think the first set might have even been 3 x a week.
And later when I started with chiropractor and was in severe spasms he had me come 3x a week till we got the spasms resolved.
*My first sets of PT were only focused on the hand, wrist, elbow, arm pain as it was a w comp claim and nothing beyond that was addressed.
Finally got sessions for chronic shoulder/neck strain later on and more of the rsi pain/sx resolved with PT on the neck & shoulders....
Soon after that was when I started to find info about TOS.
*** did PT say to be sure to drink lots of fluids, tx can cause toxins and crud to flush out of the clogged up system, and water helps to flush it out.
Also could be delayed pain due to the pT session and the movements. If it get really bad call the PT place and let them know you are in quite a bit of discomfort.
They may say to come in for some gentle modalities.
Did they do any heat, ultrasound or massage, or e stim before or after the rib mob work?
My PT session /and chiro all used heat, massage, e stim BEFORE doing any other therapy.
It softens & loosens the tissues so they release more easily. That is what they all told me and it made sense to me.
Often I would go home and use ice after the RSI ( hand/arms) PT sessions, but ice/cold didn't feel good at all for my neck/shoulder stuff.