Since around a week or so I have a weired problem with my internet connection through a 4G SIM-card in a TL-MR6400 router.
Certain websites won't load (e.g. dropbox.com, some news websites), while others are just fine. I have the same problem on multiple different connected devices (Mac, iOS, android), and also some news apps won't load new data.
Interestingly, when I try to access the same websites through my work proxy connection, they load just fine.
I installed the latest firmware, switched off parental controls of my internet provider ... no luck.