Make sure you do the OCLT first before deciding to raise your CYA.
There is nothing magical or absolute about CYA levels and honestly a pool can be managed with a CYA anywhere from 30ppm to 100ppm. The critical bit of understanding is that it is the ratio of FC to CYA that is important! You need to maintain a 7.5% ratio as per TFP recommended levels. Chlorine loss decreases with increasing CYA and so you may find that once you balance your FC/CYA ratio properly, a higher level of CYA makes it easier to maintain your set point without losing too much during the day. You'll only figure this out through rigorous testing and so it is important for you to test and dose daily for a while so you can get to know your pool's needs better. The PoolMath App is a great way to dose and track all of your pool data.
On top of doing an OCLT test I would test FC about 30 minutes after adding chlorine to see if it went up as it's supposed to. Pool math is very accurate provided pool volume is correct and chlorine strength is right. And according to pool math a gallon of 10% chlorine will raise FC by 8ppm.
You may simply have chlorine that lost some of its potency.
On top of doing an OCLT test I would test FC about 30 minutes after adding chlorine to see if it went up as it's supposed to. Pool math is very accurate provided pool volume is correct and chlorine strength is right.
I'm sure that this has been stated before, but I hae not read this. An epiphany to doing this, is after you pass an OCLT, which by the way OP said he did in his first post) If you do the 30 minutes test that you state, and do it at dusk when sun effects are gone, you should be able to use pool math to give you a somewhat accurate volume amount for your pool, maybe more accurate that normal volume calcs.