@Clive_A 
Thanks for replying.
The instructions you referred me to i already tried, also tried other tutorials/instructions from this community website.
I also tried suggestions by people with similair problems outside of this website (that is why i edited the VLAN interfaces UNDER the config of the switches in Omada, which haven't seen in the instructions you referred me to). 
And that is why i decided to open this thread.

I am not sure if i have tried all relevant tutorials, If you have another tutorial i can try it is always welcome.




 

  @wkas 

to set a vlan on a switch you have to select port not config

  @MR.S 
Thanks for replying.
Sorry, one of my first images in my original post was not clear here! 
The first thing i did everytime, was assigning the vlan to the port i wanted on the switch.
That is what i meant with this:

" This is the port on the switch i am assigning VLAN200 to. "
 

  @wkas 

if it doesn't work, you have something between the router and the switch that destroys the vlan. be sure that the switch is connected directly to the router and to a port that has vlan200 enable on router.

and do not set pvid on port on router. pvid on router have to be 1

  @wkas 

and update the router to the latest version, the version you are using is outdated and full of bugs.

You can find the latest version here

https://www.tp-link.com/en/support/download/er605/v2/#Firmware

  @MR.S 
Thanks again for replying!

I have pulled apart the physical network setup and checked if anything was in between the router and the switch,

but this was not the case. Everything has been put together again, but the issue did not resolve itself.

Then updated everything to the latest versions (Controller v5.14+, Router v2.2.6, Switches v1.20.1), but the VLAN issue persists.
(I did the router upgrade from 2.1.2 to 2.2.3 before, but that bricked my whole setup thus had to revert back)

The only thing i can come up with now is to do a full factory reset,

but if you might have a suggestion for something i did not check,

please do let me know!
 

  @wkas 

It's really quite simple.
1. create a vlan interface on the network, mark all interfaces as active for your vlan.
2. connect the switch to the router, make sure that the port config is profile all on the link to the router
3. to untag a port, go to port config, select port and select vlan200

have you configured switch ACL disable all switch ACL rules

you must also check that you have not set PVID on any of the ports on the router.

If it doesn't work then I don't know what is causing problems for you.