can´t activate

Hi,

I installed and deleted the plugin a couple of times already, but every time I get the same: I click on “activate”, and then I get a message on a banner saying that the plugin has been activated, however:

– the plugin (in the list of plugins) still shows the option “activate”, as it was still unactive (instead of showing “settings”)
– I can´t find the plugin under “appearance”, or anywhere else, to assign the 404 page that needs to be used.

I already had the Permalinks to something else than “plain”.
I´m using Divi´s latest version.

I would be grateful for your assistance, thank you in advance.