I hope that I would not need to write this message, but after it happened a second time, I feel the need to reach out.

Short background:  I am running Verizon FIOS 100Mbps/100Mbps connection (using CAT 6 cables):
1) Verizon ONT box connects into Actiontec WAN Port (this is the Verizon Router, which has all WIFI disabled acting in BRIDGE mode.  I need it for VOD, Channel Guide, etc as I have the TV/Phone/Internet package)
2) Actiontec LAN Port goes into AX11000 WAN Port
3) AX11000 LAN Port goes into the PC

After upgrading to the AX11000 five weeks ago (including latest firmware1.0.5 Build 20200216 rel.72186(5553) ) -- All seemed to work just fine, however about a week later, my DOWNLOAD internet connection on the HARDWIRED PC (nothing to do with WIFI) would almost slow to a crawl (running at 20% of normal speed), but the UPLOAD connection numbers remained fast   After numerous tests, including one that I plugged in my Laptop directly into one of the the LAN ports of the Actiontec Verizon Router, therefore bypassing AX11000 -- my DOWNLOAD connection was shown and confirmed to be normal (FAST at around 95/Mpbs).  This clearly confirmed that the issue is somewhere within the AX11000.

After speaking with TP Tech Support, I was advised that I factory reset the AX11000 (then re-setup my settings from scratch).  I did that and my connection went back to being normal (FAST).   This lasted for almost 3 weeks again but last night, I noticed that Youtube videos were getting stuck on various devices (including the HARDWIRED PC), and I decided to re-run the internet speed test.  Low and behold, again the same exact problem was diagnosed.  My DOWNLOAD speed was 80% slower than normal, while my UPLOAD speed was running at FULL speed.     Please do remember that Verizon FIOS, unlike cable, always keeps the same speed -- no matter how many people are logged in.  The nodes are not shared, so you have a very stable connection and speeds don't change.

So, with my speed not being correct, I screen captured the following screens for you to see:

Here it should be something like 90-95 Mbps for DOWNLOAD speed, but it's only 16 Mbps: 



The next screenshot shows the HISTORY of my Speedtest checks.  One can clearely see that from May 19 up until June 7, each one was at least 90 Mbps:



And this next one is from me running the Speed Test using Verizon's test site from my AX11000.   Please keep in mind again that all of these above results are for a HARDWIRED via CAT6 cable internet connection and nothing to do with WiFi:

Notice that the UPLOAD speed is always FAST & CORRECT in all 3 of the above screenshots.

Few hours ago, I decided to Turn OFF the AX11000 router and shutdown my PC for 3 minutes.  I did NOT touch the Verizon Action tech router, so it kept running.   I did NOT RESET that AX11000.  Just turned it off.

Upon turning back the PC / AX11000 my numbers have returned back to normal (FAST DOWNLOAD SPEED):
 

and...

and lastly, Verizon's own Speed Test confirms that all is running FAST:



So this is the problem that I am having.    It seems to creep-up every few weeks. I have run the same FIOS hardware for the past 5+ years, and never had such a problem with the Linksys EA9500 WIFI router that I had before getting the AX11000.   It cannot be a bad cable, as all it took was turning the AX11000 OFF and then back ON to fix this issue.

If anyone has an idea, suggestion on how I can avoid having the need to MANUALLY turn-off / turn-on the AX11000 every few weeks, that would be much appreciated.  Otherwise, EVERYTHING works beautifully on this router.  I have streamed numerous 4K movies, have 8-10 devices running at the same time on WiFi, multi-video conference calls and all without any WiFi failures.  But if the AX11000 is only getting 20% of the supposed download speed, of course all WiFi devices also get effected.

Thank you all for your input.