Device: RB951Ui-2HnD

Initial software: 6.4x.x (not sure what the exact version was)

Upgraded to: 7.6 (POE started at boot with no eth connections)

Since: reverted to 6.49.7 and 6.48.6 and no luck turning it off.

Then resorted to netinstall and no luck either.

I have thoroughly cleaned the board and visually inspected the port for dust but nothing.

Anyone else?

The PoE is never off?
Try to upgrade (downgrade) the RouterBOOT. ( 2 subsequently reboot needed after you downgrade the RouterBOOT... )
RouterOS is not the only software inside the RB than go updated.
Also the internal RouterPoE firmware will be upgraded, on old 5.x is a manual operation, but after 6.x the update is done automatically.
Probably the updater check first if the RouterPoE firmware is more recent or not, and if it is, do not downgrade to v6

RouterBOOT is the same thing as the firmware version number found on the RouterBoard page in winbox?

Yes.

RouterBOOT is the code that start the RouterBOARD,
RouterOS is the... OS loaded by RouterBOOT,
"RouterPoE" is the firmware inside the PoE chip (not all PoE devices have it's own PoE chip)
"RouterLTE" is the firmware inside some LTE modems.
Various other firmware types are on Wireless chip, USB chip, etc. etc. etc.

I have downgraded ROS to 6.10 with firmware, 3.12, rebooted twice to make sure it has taken.

I have no config on this device other than trying to get the POE to turn off with no luck. I have requested a print at CLI and it states that the port is port 5 poe is auto-on. Then turned it off via CLI and the POE remains on.

should I back-date the firmware version even further?

Will a supout help you get a clearer view?

If you go on system/resources on latest version is displayed the factory software version, you can downgrade till that version.

I have now surrendered to the war in my head trying to fix it and accepted this device as a working unit except for the POE unable to turn off.

I've gone as far as 5.26 and the firmware wont come down lower than 3.12. to 3.08.

I'm reverting back to 7.6 for use in my local network as long as no non-poe shit gets plugged in on this port.

Wondering if anyone else has experienced this.

if you can go to 5.x you can manually force downgrade the poe firmware with
/interface ethernet poe settings upgrade
but I do not have any RB so old where test the command.

Do not mix routerboard firmware with poe firmware, as already wrote are two different things.

Firmware currently sitting on 3.24 Factory version is 3.22. I downgraded to ROS 5.26 and the firmware to downgrade to is 3.08. but not taking effect, also not expecting it to since the minimum is 3.22. but I don't think the PoE firmware upgrade is taking effect. I have teamviewer on the machine I'm executing the netinstall if you're interested in having a look.