Rear axle overbraked (picnic)

Hello together, have a new problem with my 97er Picnic. This has ABS and as far as I know no load-dependent brake force distributor (LSPV) on the rear axle. For a short time the rear axle is immediately blocked with a slightly sharper brake and then the ABS starts to regulate. I do not have to drive fast. Already at approx. 30-50 km/h a little stronger stepped on the brake, already it squeaks at the rear and the ABS regulates. The whole happens well before the front wheels start to br The whole thing started about 1-2 weeks ago. I noticed it when braking before a traffic light. Now it gets stronger and comes almost with every slightly stronger braking. About 9 months ago I had a fixed brake cylinder at the front (cuff of the guide bolt was torn, therefore water penetrated, guide bolts rusted and clamped). After a freeway ride the rim was hot and steamed. I made the brake caliper again popular and with new machines. For safety I was also connected to the TÜV and had the braking effect checked. All values were ok. Also a month later at the HU the brake values were impeccable. What could be the overbraking of the rear axle? Thank you and greeting, Niko