Since this morning everything just takes forever to load. YouTube keeps buffering, and even scrolling through Instagram lags. I've already restarted the router, but nothing helped. Telekom says the line is fine. Could it be the WiFi or the router itself?
How far away are you sitting from the router, and are you only using Wi-Fi or also a wired connection?
The problem often actually lies with the Wi-Fi itself, not with your connection. Even if Telekom says the connection is okay - that's true, but only on paper. Plenty can still go wrong between the router and your device. Try connecting with a cable directly to the modem (if that's possible) and see if YouTube loads smoothly then. If it does, the Wi-Fi is definitely the culprit. It could be interference - other networks nearby, a microwave, baby monitor, stuff like that messes with it. Or your router is just overloaded if multiple devices are connected at the same time.
A few other things to try: Check your router settings and see which frequency you're using (2.4 GHz or 5 GHz). If it's 2.4 GHz, try 5 GHz instead - there's less interference there. You also shouldn't put the router in a cabinet or behind a door, Wi-Fi doesn't deal well with obstacles. And if your router is already a few years old, it might just be getting slower. Sometimes a new one is the only thing that helps.
the problem could also be on your device itself, not just the wifi. if telekom checked the line and it's ok, then you need to see if your phone or laptop is downloading something in the background. windows likes to do system updates you don't notice, or apps quietly load stuff. have you checked that?
it's also possible too many devices are connected to the network at the same time and eating up your bandwidth. neighbors with weak wifi passwords, kids streaming, smartwatch syncing - it adds up. check your router settings to see who's all connected. and on youtube specifically: if you're watching in 4k and your connection isn't super fast, that can just be too much, even if everything's technically fine.
if it's really just the wifi that's problematic, try a different channel in the router. some devices get stuck on congested channels. 2.4 ghz is often super crowded in apartment buildings. if your router can do dual-band, just use 5 ghz if your phone supports it - there's often less traffic on it.
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