I've always used TWRP, and from quite a while, I chose not to install it, to avoid updating problems, just boot temporarily when needed. With A12 I never managed to use it through the device screen
It surprises me, that we do not have an official recovery for our device. I know how it works, and I'm not a developer that could contribute, so that's what it is.
Then I discovered OFOX, that decrypted succesfully A12, but as you have already pointed, is failing to do it on A13.
As I'm new to it, and this is not an ETA for the developers nor similar, do you know where is the problem, the chances to fix it, and on your experience from previous OFOX, how could it take to be fixed?