potiontest:
    delay: 1
    items:
    - SPLASH_POTION:16421 1

this gives me a missing texture item

same as /give and /i

EssentialsX version (/essentials):
2.0.1 b510 as of 210494d
Server software (/version):
Paper version git-Paper-1167 (MC: 1.12) (Implementing API version 1.12-R0.1-SNAPSHOT)
EssentialsX config (if applicable):

I assume you mean build 501, not 510.

As far as I know, splash potions (still) aren't supported by EssentialsX, though I may be wrong.

they worked in 1.11

What about POTION:16421?

eyy that works

found out this doesnt though:

SHIELD 1 basecolor:1644825

in 1.11 was a black shield

If the shields are still an issue, please create a separate issue.