fios going nuts wired; not wirelessly

I have gigabit fios in Brooklyn New York.
Solid for years and years.
Until two weeks ago.
My two computers (both Asus motherboards with i9 10th generation cpus) are wired to Verizon's latest router (the round white one). Running Windows 10 all upgrades.
Strangely on both machines the speed fluctuates from ~ 900 up/down to 90/90 up/down.
BUT
Wireless the situation is better: ~ 220/220 up and down.
And sometimes the connection fails all together.
Flummoxed.
BUT (AGAIN)
I suspect the router which was upgraded a few months ago.

Am I right?

Thanks in advance.

yes, that's right.
The Verizon speed test gives me perfect scores "up to" the modem (920/920).
After running diagnostics they are giving me a new router.
I bought some super cables and they didn't make a difference.
I now suspect that the router lan ports are flaky with some shifting value (high speed or not) over the day.
We will see.

rboris said:

I have gigabit fios in Brooklyn New York.
Solid for years and years.
Until two weeks ago.
My two computers (both Asus motherboards with i9 10th generation cpus) are wired to Verizon's latest router (the round white one). Running Windows 10 all upgrades.
Strangely on both machines the speed fluctuates from ~ 900 up/down to 90/90 up/down.
BUT
Wireless the situation is better: ~ 220/220 up and down.
And sometimes the connection fails all together.
Flummoxed.
BUT (AGAIN)
I suspect the router which was upgraded a few months ago.

Am I right?

Thanks in advance.

If the speeds on both go up and down consistently, yes the router is having an issue. Could be a setting, could be just buggy firmware, etc

in fact it wasn't the router but the switch. changed it and all is well.
thanks to everyone.