Windows 10 Pro 32-bit users can't logon to domain.

You cannot upgrade from Windows 7 Home to Windows 10 Pro in one step. You have to upgrade and then purchase / apply the Pro upgrade. Did you do this? Have you checked to ensure it is Pro. This was Computer 1.

I am not clear what happened with Computer 2 (wipe / install). I did not see where you said.

I haven't used or have any clients that have used 32-bit operating systems since 2007. Is memory a limitation?

How much memory is in use for the 64-bit machines?

Yes - went to home, then Pro. It is in-fact showing Pro and activated. Computer1 is 32-bit because it was Windows 7 Home 32-bit. Computer2 was basically a fresh install from the same install media but not an upgrade.

Possibly their local user account has been changed to a Microsoft account
Check in the account if it is listed ( log in with a local Account) under Microsoft Account. If so change it back to local User Account

Merete - there is only one "local" account on that computer, but would that effect domain user account logins if it is set to a "Microsoft Account" since its a local account?

Depends if there is a different password used for local account and the network (domain)  to the Microsoft account. As you may know now W10 is emphasis on Store apps and one has to log into Microsoft account to access them  hense the profile change.
They are all listed in the start menu side panel
Nothing should have changed with the upgrade however I found W10 is difficult with W10 Home verses W10 Professional networking
Can you check if the home is in the same workgroup or homegroup? as W10 Prof
Have a look in This PC >properties>Computer Name, Domain and Workgroup  settings>click on change settings.
Have you checked the sharing options?
Working with another EE member's question here lets see if they get any solutions we can use here
Auto Logon fails when connected to the network Windows 10
https://www.experts-exchange.com/questions/28958098/Auto-Logon-fails-when-connected-to-the-network-Windows-10.html?anchorAnswerId=41748709#a41748709

Merete

Sorry to hear it xsys2001i, same here I just ended up going back to windows 7 reinstalled all my software couldn't get the image backup I made of windows 7 to run so did it all manually.
I kept windows 10 on one and restored windows 7 on two. I need my systems running without problems.
Unbelievable windows updates again like 300 or more.
Windows 10 is getting the anniversary update with it being around 4 gig it is slow downloading en-mass worldwide so users may notice a few changes happening with their systems slowing possibly.
Microsoft rolls out a cumulative update for Windows 10 that might cause your PC to run 'abnormally slow'
http://betanews.com/2016/05/10/win10-cumulative-update-abnormally-slow/
Fix Slow Internet After Windows 10 Anniversary Update, Here’s How
http://www.redmondpie.com/fix-slow-internet-after-windows-10-anniversary-update-heres-how/

Did you know windows 7 support will be around till after 2020 so no need to upgrade at this stage.
Windows lifecycle fact sheet
https://support.microsoft.com/en-us/help/13853/windows-lifecycle-fact-sheet

Once you have upgraded to W10 your systems are registered  so using the media creation tool you can upgrade later so long as it is this same system
https://www.microsoft.com/en-us/software-download/windows10/