It's interesting you shared this because from my experience, I've noticed a sudden decline/"hang" in network connection-speed if I don't reboot my router occasionally and because I'm in the midst of making physical and technological change in my office/home, I was going to get to the root of that issue when I'm finally able to sit down and look at it. My network is pretty much composed of 4 laptops, 2 desktops (Windows and Apple based OS), smart home system (Hue, Chamberlain garage, Ecobee, etc), 2 iPhones, a couple iPads, Apple TV, commercial based network printer, a couple NAS HDD's, PS4, a network based video phone system (a higher grade video conferencing equipment for Deaf/Hard of Hearing individuals like me)... and once I sit down to focus on the particular problem, it means I'll have to make all of the configurations to the aforementioned equipment and the only person living in this unit outside of me, is my S.O. and... let's say, I'm waiting until she's busy with work and out of the house then...
Regardless, as I was thinking about your issue, I was wondering if you bought or rented your own modem from the ISP because one my earlier mistake was using the incorrect ethernet cable (CAT 5) from the modem to the router that was hindering the speed, in which I ended up switching over to CAT 6 Ethernet cable (does make a difference in one aspect) but also, I've learned to basically set up my router to "reboot" the router everyday at midnight because if I don't, I see the issue as described above to be much more prevalent...it seems as if the router is working overtime (processing data) whenever the modem is providing a new IP address that the router just can't..."kick-in" or "refresh" to reflect the speed better.... with further consideration.... have you updated the firmware on both, the router and the Intel AX200 (there's pretty recent firmware update that was released last month for both devices and in the release notes for both of them seem to touch on the areas we're looking at...). Finally, not a lot of people realize this, wireless network speeds can be affected by simple radio interferences that has nothing to do with the network, for example, microwave interference, the A/C unit has a mechanical device that emits a slight signal (I haven't figured out what it is but...) that'll make some older wi-fi devices act wonky and in fact, if you look at a regular led bulb, it actually emits radio-waves (not the smart bulbs, regular bulbs) that actually used to disrupt my old D-Link DIR-868L router if the lamp/lightbulb was placed within 3 feet range of the router that I had to adjust accordingly. Then there's the issue of placement of the router/devices that can hamper signal issues (no one realizes that a router should be placed as high as it can be to disperse the wifi signal better to all devices so they just put the router on a table/tv stand/desk) or in my case, I live in Chicago and my wifi signal has a hard time penetrating plaster walls than the current conventional dry wall....
I wanted to share my thoughts and see if this helps and I apologize in advance if this a bit too much for you but... let me know what you think...