Commands such as /test pos search within a range of up to 200 blocks (plus a duplicate range of 15 blocks), meaning a server that runs this command without a nearby test instance block will be very slow. This is because the command checks block states in an non-optimal manner.

The effect on the game is that it's very easy to slow down and eventually crash a server by putting /execute as @p run test pos x in a repeating command block.

This issue could be mitigated by using the Chunk#forEachBlockMatchingPredicate method, which should be a lot more efficient as it checks the palette of chunks rather than scanning the chunk's block states. It all goes full circle