'Lagging' internet connection

[#1]

I've had broadband in my new house through Plusnet for about a month now, and have been experiencing a strange 'lagging' when browsing the internet on all my devices (phone, laptop, tablet etc.), loading content on mobile apps, watching content through streaming services on my smart TV and when trying to have a video call (Google Meet, Teams, Whatsapp etc.). It's like it needs to warm up before working!! Even when loading any Speedtest website I experience this lag of up to 1 minute before the website actually opens. When it does, the speed test delivers results which are within the expected range.

Sometimes it gets so bad that I need to reset my modem to get back to a connection that works, even though there is still a lag.

On very rare occasions I experience a great connection, but this does not last long.

Connected my modem to the test socket without any improvement. Got a new router from Plusnet which made no difference. Tried various 'channels' try avoid interference in my wifi - no improvement. Got an expensive wifi mesh system that selects optimal 'channels' automatically and ensures there are no dead spots in my house - no change. Connected laptops via ethernet cable and experienced the same lag.

Any idea what I can try to solve this?

I'm on my mobile data most of the time!!

[#2]

Moderators Note
This topic has been moved from ADSL Broadband to My Router.

[#3]

Thanks for your post @stefanbez01 

I'm sorry for the issues with your connection. I've messaged you back via Facebook just now asking if you've split the 2.4GHz and 5GHz wireless frequencies into separate wireless networks, and if you have, which one do your devices connect to when you have issues? 

Having read your post though you've mentioned you experience lag on a wired connection too. Do those laptops you've tried plug directly into the router or through a switch or powerline adapter first?