Sorry for posting that issue twice, but it has been classed as "Unable to reproduce", so here's how to reproduce:

• /say @e (you should have a list of all entities, the first of them being players, including you)
• /tp 100000 120 0 (you teleport yourself far away from where you are)
• /say @e (you should once again have a list of all entities, but without you!)

This breaks some of my command creations as I cannot execute commands or grant advancements to players who just teleported, which might be problematic

Notes:

• You are still triggered by @p and @a
• It does not work only with /say (at least with /execute and /advancement but it sounds like it has nothing to do with the command used)