Nextcloud (via Marketplace) suddenly not reachable via custom domain

Hi together,

I have the following problem: As I have little to no understanding when it comes to development but care about privacy, I yesterday decided to set up my own Nextcloud via the marketplace one klick option here.

I have managed to set it up and also set it so I can reach it via my domain I purchased at namecheap. There, I set the domain to point to the name severs 1 to 5 of linode. Everything worked fine, both me and my girlfriend where able to reach the cloud via the domain.

Until about an hour ago, where my desktop client suddenly disconected. I also cannot reach my Nextcloud to the browser. It sais that the website is not found. When I try to connect via the IP of the adress, I still get to the cloud (but not access is granted since I get the trusted domain error).

I therefore suspect there is something going on with DNS, but I have touched NOTHING (I swear) and, as mentioned, have more or less no clue about any of this.

Does anybody have a solution to this problem or maybe an explenation what is going on? Please, be patient with me an use simple words, I am not a developer as I mentioned.

Thanks in advance!