Have you tried doing a speed test during this time? It could be latency, strain on the connection, packet loss, all kinds of things. Also make sure you have the mod "player list plus " turned off as it can cause all kinds of latency issues.
Are you going off the in game ping? Cause that takes a lot of other things into account, CPU, ram, etc. A lot is dependent on the host. Which is why my wife and I went from around a 10 ms ping to 30-40 while sitting right next to each other after they changed how it records ping.
I recommend you continue to press your ISP about this, especially as this is only an issue at a set time. I had similar problems at home, with BT, but only with our WiFi. Changing WiFi channels ultimately solved it.
That doesn’t matter. I lived in an area with less than 2,000 people and had a fiberoptik line. Still got all kinda of problems. Turns out when I upgraded my Internet, they forgot to switch over a protocol on their end. I was still on PPoPe instead of PPTP or something. I don’t remember all the terms. Either way, it caused all kinds of issues for me, but strangely enough, always around a certain time. The IP company thought it was someone with a old radio or something which can apparently cause issues. Basically thought there was someone with a radio hobby causing issues.
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