I see all these issues with the lack of 2.5gb support.

But i have had issues with using 10gb sfp+ connecting to some of the other models and it has not mattered which mikrotik was on the other end.
What successful brands and fiber types have people been using.

What i get is a lot of flapping (reconnects)

I have used the same models that were working between two other connections without luck.

Colored 10G SFP+ Twinax Cable, Direct Attach Copper(DAC) Passive Cable in Green, 0.5m (1.64ft), for Cisco SFP-H10GB-CU0.5M, Meraki, Ubiquiti, Mikrotik, Intel, Fortinet, Netgear, D-Link https://a.co/d/iR5HhYR

Looks good.
My issue is that i am nearly 30 feet between that device and the other endpoint in the basement.
So I have been using SFP+ and fiber. If someone has a suggestion for DAC that is long enough that works, that is fine.

But it seems weird that only this device seems to have the problem.

No DAC is that long. So yes, using a pair of SFP+ modules and fibre run is the way to go.

MT is notorious for flakey support of SFP/SFP+ modules. That is sometimes even true for own modules, let alone for 3rd party modules. Here's compatibility table, but clearly doesn't list all possible combinations.

I certainly hope somebody gives you information about optical modules which are proven to work fine with RB5009. It seems like their own MM SFP+ module should work fine.

That was very helpful. I am going to try INTEL FTLX8571D3BCV-IT from the list first, as Amazon has them at 20/ea as opposed to 60/ea.

Getting a pair so that i have the same on both ends.