Downgrading from 2.9 to 2.8.4 stretch

I've ended upgrading to 2.9 on buster, to see if I can sidestep some issues. I am using some functionality on the lathe not available in 2 8 (which I forgot about) single count encoder plus switch on homing. Thats where the custom firmware comes in. I will close this and work through issues as far as possible. Ill see in the am if this resolves the above. As always thanks for the help, appreciated.

Can I ask for kernel?
uname a

I've tried a few over past few days on the different install. This buster install is on 4.19.0-23-rt-amd

I managed to get the router to launch, testing dry run code as we speak. Upgraded the networking cabling too. Not sure if this solves the issue, we will see.

No idea if the lathe setup launches yet, will test that soon. im taking it one thing at a time

Edit. Lathe launches too. Very strange. Seems in my case downgrading to 2.8 is not a good idea as i. Using some 2.9 specific config. But thankfully, both machines are moving now under the latest 2.9 on buster so we will have to see how it tests out over next couple of days. Big thanks to all in the community, i was not looking forward to configuring those machines again. Ill update my other thread with NIC related findings.