Broadband speed DROPS dramatically after every Zoom call

[Xopherhead]

The speed of my broadband drops by a huge amount after I finish a Zoom call. From 40 meg down to as low as 0.2 meg download. Closing Zoom doesn't make any difference. The only way of getting the speed back up is to restart the laptop which is obviously a massive pain. (Or it does come back after 10 mins or so if left). Initially I thought the problem was with elsewhere and have had the router replaced, had an engineer out etc and can confirm everything works and I have a fast connection. I can see there has been discussion about this issue in the past but couldn't see a satisfactory solution. Any advice appreciated! Thank you.