APC UPS not switching PC to battery backup. Cannot run self test either as the PC shuts off.

[BiteyIT]

Equipment: APC 1500VA UPS Battery Backup BX1500M

PC: AMD Ryzen 7 3800X 8-Core Processor 4.20 GHz, 16gb RAM, NVIDIA GeForce RTX 2070 SUPER, 750 Watt - Thermaltake Toughpower PSU, running Win 10.

Problem: For the past 15 months I have been dealing with random shut offs of my PCs. House lights dim as well, so I thought it was an electrical issue. I have worked with 2 electricians and my power company. I have had these entities replace my electrical panel, install a home surge protector, change my outside meter and small transformer in my yard, installed a smart reader to monitor the line for 2 weeks, and trace the line back to the substation. All of this to no avail. The smart meter noticed amperage spikes, but the times did not coincide with any of my shutdowns (I wrote them down during that period). Both electricians ghosted me for reasons I cannot fathom other than it being a difficult job to diagnose and fix. The last solution  discussed was adding a dedicated circuit and running a larger gauge of wire as they seemed to think it was a voltage drop due to the distance between my office and the panel being over 100'.

I began looking at an UPS option in the last three months. The first purchase could not support the load as it was only an APC UPS Battery Backup, 600VA BE600M1. More recently I have purchased the above unit and still experience multiple daily shutdowns. I am at a loss as to what to try next. I have scoured Google and found similar issues, but their fixes either did not or would not work for various reasons (different unit, . 

When the PC shutdown happens, the router and the monitor both stay on as they are both plugged into a battery backup socket. The backup itself does not turn off either.

My questions are: What am I missing? Is this just a bad battery or unit? Is this actually an electrical/electrician issue? Is my PC PSU bad/faulty? Is there a BIOS or PC setting that needs changing? If more info is needed I'd be happy to provide it. Any help offered would be greatly appreciated. Thanks.