[Marttt]

Is easier sharing the .sp because your log differs from the lines from the main post, unless you downloaded from another post/page

Btw "Client index 0 is invalid" is really easy to fix just by adding a "if (client > 0)" in most of the cases
In your case seems that it throws when the damage came from the worldspawn entity for example (fall damage)

And for "Entity 18 (1 is invalid" is like the same, just add an "if (IsValidEntity(entity))" before.

Everytime you mess with timers you must check if the client is valid, cause it can be disconnect/destroyed during the delay.