I think that borates are best done when everything is really well balanced and stable, you may want to hold off until someone here says that it is time. I have no experience with that.
CYA of 50 is near perfect. I suggest taking the remaining tabs out of the feeder and letting them dry out for later use. Run to Walmart or Sams or the grocery store and get some unscented bleach. Use that going forward. Expect pH to jump up when you stop the tabs, so be ready to start monitoring pH and TA. Have Muriatic acid (or dry acid) on had to adjust pH.
Depending on your CH levels, you may be able to use cal-hypo. It is economical in the huge containers from a pool store, keeps a long time, so good to have on hand.
When I was using tabs as well as bleach, I found that when the FC in the pool was kept in range which for me was 3-7ppm, the tabs were very slow to dissolve. Maybe they go faster at low FC levels, I don't know. It suggests to me that you don't need to worry about some sort of malfunction in the equipment.
If you choose to keep using the tabs, you can at least calculate what the CYA will be after so many more tabs. Just know that there may be some CYA in the pool now that is too fresh to show up on tests yet. So your test of 50 may be 55 or 60 already, hard to say. Then you add whatever the CYA is in each tab in the feeder now. For my pool, each tab adds about 1 ppm of CYA, your pool is smaller and so will be a larger ppm per tab. Keep that predicted value in your notes and use it for determining FC for normal operation and for shock levels.