Issues with TWRP 2.8.6.0: Flashing a different Modem

It's possible this is also somewhere else, but I am having trouble finding it....so I gave up and figured I'd ask.

Okei. I started with TWRP 2.8.6.1. So from my understanding flashing a modem does not work in versions of TWRP newer than 2.8.6.0. I get that, and so I decided to downgrade. However, that seems to be the version that I am unable to get working. I've attempted to flash the 2.8.6.0 recovery via fastboot. Everything says it's good in my terminal. So I go ahead and boot into recovery, but my phone goes to a black screen for a moment and then reboots into OS. I tried a different method, via the app from the google play store. It tells me that there is an error of some sort, or that I already have it installed. So I used the google play app to install 2.8.6.1, which worked flawlessly. So now I am back where I started.

Is there some trick to getting specifically TWRP 2.8.6.0 working so that I am able to use it to flash a different modem? Will using an even earlier version yield the same results? Or am I better off doing it via fastboot?

Thank you for your time <3