Minecraft Version: PaperSpigot 1.12.2
Skript Version: I tried dev33 and dev35b and it works on both
Bugged Code:
command /bug:
trigger:
set {_test} to "hi"
set {_testing} to "hello"
replace all "hi" with "hola" in {_test} and {_testing}
broadcast {_test} and {_testing}
Evidence:

Working Code:
command /works:
trigger:
set {_test} to "hi"
set {_testing} to "hello"
replace all "hi" with "hola" in {_test}
replace all "hi" with "hola" in {_testing}
broadcast {_test} and {_testing}
Evidence:

Explanation:
Basically, if you specify more than 1 variable to replace something in it'll change the rest of the variables to the value of the first variable.
Sounds like it could cause notable problems when working with lists. Thanks for the clear report!
Yeah, it was hell to debug, took me like an hour and a half to figure out why my variables we're the same value.
It broke when Tuke did some updates a long time ago, reported it as well but nothing happened. He claimed it wasn't him.
@TheLimeGlass You added support for replacing in multiple texts in https://github.com/bensku/Skript/pull/177 and merged in deb20b. It didn't even work between dev20 and dev23 (It gave this error) i doubt the PR is even tried, because you just added s to the expressions, also not to the right expressions. At least it didn't give any error since Tuke's fixes. So the bug exists since your PR.
Well I will look into fixing what he changed then.
Most helpful comment
Well I will look into fixing what he changed then.