Cannot connect to WiFi network. AssociationFailure on log records

It's most definitely not the answer you want to hear, but your WiFi died. It happens.

What was key here is that you attempted to connect to an unsecured network. One methodology I try to teach to new techs is to take things down to the "lowest common denominator." Getting connected in a basic state (like with no security) establishes a baseline - there are no other factors that could get in the way like keys, certificates, etc. If you can't connect there, you have a physical issue.

Next, you tried a different network router. If the problem exists in two different places, the odds of it being your network go down substantially - like next to improbable.

You did go a bit beyond in your diagnostics, though...so just some feedback for the future:

• resetting the WiFi router is good, but not entirely necessary. Hypothetically, if you didn't own the network you wouldn't be able to reset it.

• changing the SSID and/or password. Not necessary. The SSID is just text and the password is just a key. The radios in the access point (router) and in your iPhone don't care what text characters are being broadcast that identify the network. Doing the unsecured network addresses this

• forgetting the network and rejoining. This is excellent. Doing this in conjunction with the unsecured network will tell you a lot!

• multiple routers and ISPs. Excellent on the different router (as elaborated above) but it's not necessary to change an ISP. The radios don't care if you use one ISP over another the same way your car doesn't care if you use one interstate or another.

All in all, excellent diagnostic work, but undesirable diagnosis. It looks like it's time for an upgrade.