Very strange problem. Couldn't find it on any website (Please help)

Hey Everybody,
I have a very strange problem with my whatsapp. I'm using a LG G4.
The problem is when I try to send messages, they just disappear from the screen, then about a minute or two (the length changes; it's not a specific time period) after trying to send the messages they suddenly appear back on my screen and being sent. At the same moment I can still recieve messages, but not send. This happens a lot, not always, but statistically about 8 out of 10 times i try to send a message.

Another problem (I'm sure it's related to the problem I mentioned above) is with media I'm trying to send OR download - when i try to send or download media (voice messages, photos, videos etc) they would download fully and in the end do the "full circle" like when it's loading (I just can't describe it but i hope you understand what i mean) and take time until it's fully completed. AT THE SAME TIME if i would try to send messages they would disappear from my screen as well. The media will finish downloading or uploading at the same time that my messages would reappear on the screen and be sent.

I'm having this for a few months already and it's driving me mad. I've done a reinstall + factory reset, no luck. Couldn't find the problem on ANY website/forum too.

Please help me with this.
Thanks in advance!