Hey Michael, good to have you back!
Hmmm…water damage…you know what I say in regards to latent issues :>).
I once had a similar water damage situation on a 6S Plus where everything probed okay but still didn’t work, despite replacing the LDO’s etc. It drove me nuts until I realized that the the VCC_MAIN wasn’t fully connected between the RCAM LDO and the rest of the VCC_MAIN. When I probed it in diode mode, I got a similar reading (I didn’t notice the slight discrepancy at first) but what I was reading on the VCC_MAIN pin of the LDO was actually the other downstream FCAM LDO and the values were almost the same. When I finally realized this, I tested the continuity between the RCAM LDO VCC_MAIN pin and the rest of VCC_MAIN and sure enough, they weren’t connected. The inner trace had probably blown due to the water damage.
The circuitry is a little different on the 7 series so you’ll have to dig around but make sure that there is actual 4.2V at the input of the LDO.