I am not too sure if this is hardware issue or software but I suspect software first.
The issue is, on my newly bought RB5009 the SFP+ port does not seem to work with anything SFP I have. It appears that whenever something is connected, the port status on RB5009 side is shown as active all the time trying to Tx, but fails to negotiate speed and receives no Rx; but on the other side the connection will be shown as connected for a very short period of time (could be almost immediately to about a second) and then shown as disconnected.
I've tried all SFP devices I have, including:
1) A pair of SFP (1G speed) RJ45 adapters of unknown brand
2) A bunch of more than 5 different DAC I gathered from friends
3) Two pairs of optical adapters of brand 10Gtek and HiFiber
All these are confirmed to be working totally fine on my RB4011iGS+RM and more than one Netgear Switches with SFP+ port.
The RB5009 comes with firmware version 7.0.5, but also tried to upgrade to 7.1rc6 (and later 7.1rc7 and 7.1 Testing) and issue is the exact same.
I've also tried to manually set various port speed on both sides, nothing helped.
Please let me know if there's any more information I can provide to help this. At this moment, the issue is blocking my usage of RB5009.
UPDATE:
At this moment, I am almost sure this is an issue on Netgear MS510TXUP. I've able to make other switches to work with RB5009 without issue after a few mindless tries including cleaning the whole router board and DAC with electronic cleaner, a few configuration changes, and a few times of various resets.
UPDATE 2022-03-24:
I have confirmed the same issue is here with Zyxel XS1930-12HP too.
UPDATE 2022-04-19
Thanks to @xfoxtbat we have a plausible root cause:
viewtopic.php?p=927657#p926511
It seems that the SFP+ port on RB5009 supports EEE which is not supported by the switches I found to have this issue.