I was having a problem I'd describe similarly, I was seeing brief Internet drop-outs (which makes the Internet seem really slow when it happens a few times within a minute or two.)
Like you I also rely on wireless as my only level of Internet connectivity. (I dropped DSL, because it sucks here.)
I made one small change to my hotspot settings that not only made my connection work consistently, it kicked up my bandwidth from 4-5 MBPS most of the time, to 20-27 MBPS -- yeah, 27! :-)
I fixed it by turning off the DHCP Server on the hotspot (in Network -> Router settings.) Of course this means I had to assign a static IP address to anything that connects to the hotspot (which in my case is only a router.)
The improvement was huge -- I telecommute so a fast, stable connection is critical! This thing was killing me! I've had fast cable connections for a long time before this, so I knew what a good connection was like. This one was borderline unworkable (and very, very frustrating), now it might be the best I've ever had for my home/office. Boosting performance that much was mind-blowing!
If the above was already too technical, don't even think about reading the rest, it's only the "why", all of the "what" is above. :-)
I found that the DHCP traffic generated by my mobile hotspot was causing the IP address assigned to my [tethered] PC to change way too often. My PC wasn't even relying on the hotspot for DHCP, I have a router between the hotspot and my PC doing that job. Even so, the hotspot's broadcasts and ICMP traffic were making it across the router, regularly resulting in multiple successive automatic reconfigurations -- which are disruptive and time-consuming!
I created a crude diagram of my topology for reference, but I really don't think my topology is all that significant, the hotspot behaved the same when it was USB-tethered to my PC...
No I haven't tried it over USB with a static IP, in fact I have done nothing further to test the repeatability of this problem, nor document my success... I've been enjoying it too much to muck it about.
-Mark [edited for privacy-please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc.]
{ }
{ cloud }-\/\_mobile_/\/-[Elevate hotspot]-\/\_wifi_/\/-[bridge]---cat5e---[router]->[*]
{ }
(Where [*] is multiple PC, IoT and other types of hosts connected.)