Your high TA is the primary cause for your fast pH rise and at higher pH and TA you are probably getting calcium carbonate scaling in your SWCG cell in spite of the low CH. At pH 8.0, the saturation index is +0.2. The borates help to reduce the problem, but are not enough given your high TA. The good news is that you have no overnight chlorine loss which means you don't have anything consuming chlorine in your pool like algae or organics.

Test your tap water to see the TA and if it's a lot lower then the pool then some water replacement will help, but you can also accelerate the lowering of TA by following the "add acid and aerate at low pH" procedure described the Lowering Swimming Pool Alkalinity -- A Step by Step Guide. It's going to take a lot of acid to get your TA down -- every gallon of full-strength Muriatic Acid (31.45% Hydrochloric Acid) will lower your TA by 40 ppm but you won't add these all at once. You follow the procedure to lower the pH to around 7.0 and keep it there while aerating.