What can be the result of a decrease in the abundance of withdrawal bleeding when it was always abundant on the first day of bleeding and now suddenly it is not?

For half a year I have been taking vines tablets, with each package there were spotting a few days before withdrawal bleeding (with a downward trend; about 2-3 packs of spotting occurred in the middle of the pack and later only about 4 days before the placebo tablets) and eventually spotting passed into withdrawal bleeding. I didn't want to change the tablets because they fit me and the only side effect was those spottings that occurred in fewer and fewer days. The gynecologist stated that we can stay with these tablets if the spotting is not bothersome and may pass soon. Unfortunately, with 7 packs of spotting appeared already on the 15th tablet from the package (and lasted until the day of bleeding), and the withdrawal bleeding was much less abundant than usual (color and other things as usual). Negative pregnancy test. My question is what might be the result of a decrease in the abundance of withdrawal bleeding when it was always abundant on the first day of bleeding, and now suddenly it is not.