Question Modem and WiFi confusion

[Spirit84]

Modem is connected via coax to my ISP.
2 direct ethernet connections from the modem:
a: direct to VOIP phone device
b: direct to Orbi router.
I went to sleep at night and all was functioning properly.
In the morning both devices were offline.
I disconnected the modem and rebooted. Same issue.
I disconnected VOIP and router and rebooted. Same issue.
I connected ethernet to an open port on the modem and connected directly to my PC - perfect - internet is great.
Called tech support from Orbi and ISP - no one could figure it out.
About 4 hours later, without touching anything else, both devices came back online.
How could this be?

 

[Ralston18]

My generic answer to such problems is "Gremlins".

More seriously, without a log entry or an error message of some sort it may be difficult to know how it could be.

Your ISP may have just quietly fixed something....

Could have been that some update went astray and was quietly rolled back or fixed.

In that the router seems to have played some role my thought is that an error occurred and it simply took time for the ISP, modem, router, and your network devices to all get back in sync again.

Sometimes network configurations need time to restore themselves and any interim actions by users (at any level) simply complicates and/or slows things down.

Leave it all alone and the software, by design, will sort things out.

Look in the router's logs (if available and enabled).

Window's Reliability History may have captured some error messages, warnings, or even informational events.

The messages could be any where in the timeline: beginning, middle, end. There could be multiple entries throughout.

 

[Spirit84]

Thank you Ralson18 for your speedy and in-depth reply.
I am not a techie person so providing any kind of log entry is not something that I could provide.
However, perhaps the following will help provide some clues about this puzzle.
I admit that in an attempt to keep my OP short I only provided half the story. Here is the rest of the story:
The WiFi meltdown that I wrote about above happened this morning.
Yesterday afternoon I called my ISP asking for them to check my upload speed. I am paying for up to 30mbps upload but with my Orbi (which is about 3 feet away from the ISP modem) my upload speed is only about 3mbps.
The ISP tech told me that on the phone that all signals to my modem were to spec and offered to reset my modem.
After the modem reset this is where all the fun started!
My VOIP phone (reminder: connected via ethernet to modem port) came back on line - no issue.
My Orbi on the other hand would not reconnect. The ISP tech said that was weird (they always say that).
I called Orbi tech support and they had do a complete factory reset on the mail Orbi router (reminder: connected via ethernet to the modem). After doing this the Orbi reconnected.
My WiFi worked perfectly for about 6 hours and then I went to sleep.
When I woke up.....(read my original post).
The WiFi has been working fine for the last 6 hours.
So to conclude here is my confusion:
1: the ISP tech told me that resetting the modem should not have casued any issue with my Orbi reconnecting. The Orbi tech told me that sometimes when a modem reset is done things like this can happen. Something to do with the ISP sending out new MAC or IP or something like that.
2: in any case - if everything was back to normal why the meltdown?
3: Re my upload speed: because I wired my PC via ethernet directly to the modem this morning I was able to test my upload speed directly from the modem. 30mbps! The WiFi connection via Orbi seems to be around 10-12mbps now. Is this normal?
Anyways - that is my whole story!!