Slowness effect not working when TPing players

What I expected to happen was...:
The player to recieve the slowness effect

What actually happened was...:
I tested this multiple times, the player received the slowness effect sign and it said he had slowness but he did not actually move any slower. This did not happen consistently sometimes it worked and some times it did not work.

Steps to Reproduce:
1. create a command block row that tp's the player into unloaded chucks,
2. and also gives them the slowness effect.
3. If it does not work try again, it would only work half of the time.