An Oddity in Eeveelutions?

It is an assumption, if that is your experience, but it is not fact. If what you stated were true, then no one would have a vape over 82% (outside the name trick), before the raid system was put in place. And that would make zero sense.

Btw, I have 3 vapes over 90%, evolved, and after name trick

I think you'll find that it is random. How big is your sample size?

The (61) non-forced eeveelutions that I have kept have IV ranges of:
Vaporeon 56-89 (23)
Jolteon 58-100 (20)
Flareon 58-98 (18)

Has anyone else noticed this?

No. Have two 98% Jolteons and a 89% Vaporeon for instance; just two mention three.

Yeah I have a 98 HP vape and and 94 AT vape. I can say I do not have a jolt over 88.

I've lucked out and got mostly Vaporeons with my sample size. Flareon coming in second, and Jolteon third.

However, I have purged all of my old Eeveelutions except for the OG ones that got me through the younger years. Everything is now 100% but I still evolve more Vaporeons than the other two.

Nah, it's just coincidence. I have mixed IV's eevolutions scattered all over the place. My highest CP one is a 98 Vaporeon I've had since the beginning of the game.

I had three 100% Eevees that I evolved at the same time during a lucky egg run and got one of each. (Heatwave; Thunderbolt; Hydro Pump.) Have had countless other 90+% Eevees that have evolved several various Eeveelutions.

I have 100iv in Vape, Flare, Jolt and Espeon, most of my Vapors are in the 90iv range, Flares upper 80iv and Jolts mixed 80/90iv.

I tend to only evolve high-IV, or high-CP (to save stardust if reasonable IV, 70+) and I have:
41 vaporeons
19 flareons
19 jolteons (which frustrate me since they tend to be the very highest IV ones)

I'm not entirely sure environment doesn't matter, since my ecosystem is crawling with water pokemon.