Since I use HC110 for developing TXP320 in a Patterson tank with MOD54,
I get these spots on my negatives.

I suspect they are air bubbles, but since I have never had this before, I am not sure.
The place on the negatives where I have these spots is in the bottom to the middle
of the developing tank.

Agitation is continous in first minute then 15 secs every minute. Dev time is 6min 20secs in 80ml HC110 stock solution (is 20 ml concentrate) in 1000ml of water (1 part stock + 17.5 parts water).

I hope the picture is somewhat clear. I do not have a scanner, it is a picture taken from my light table.

I have never had this with 4x5 FP4 in Rodinal in the same tank.

If it should be air bubbles, can a presoak (how long ?, agitation ?) help ?
Can it be that these problems arise with one film/developer combo and not with another combo ?

Thank you !