Efke 25 brownish stain: dichroic fog. Also pink tint
This may be dichoric fog. Try using acetic acid stop bath. While still wet the dichoric redeposit of silver can be wiped off with cotton but this can damage the image.
The pink is residual sensitizing dye. I doubt if it is antihalation dye. Anti-halation under coats and back coats ususally aren't trying to capture red light. The dye may go into solution during development and imbibe into the antihalation layer of the film. This shows poor film design but it can happen. Changing the water in the prebath frequently can reduce this. Senstizing dye is also released when the unexposed AgX is fixed. this can aslo imbibe in other gel layers.
Washing can help but it is difficult to get it out once is gets in the swollen gel. Diffusion is slow.