Any ideas? Cisco SG-300 with "Combo" port won't switch back to Fiber?

I've seen other people complain about this online, but no solutions anywhere.

Here's the situation: I have a pair of Cisco SG-300 devices (an SG-300-52P and an SG-300-28PP specifically), which have been bridged using Fiber at each end. Over the weekend, some trouble began, and in the troubleshooting process, we switched them over to Copper. HOWEVER, trying to put them back on Fiber -- nothing happens

When you inspect the Port Settings, the port is labeled as "1000M-ComboC" and there's no simple drop down to change it to ComboF. It's supposed to automatically detect when an SFP is inserted, but it's not! NEITHER of the two switches will go back to ComboF!

•The issue was not related to these ports, or the fiber in any way, it was only switched during troubleshooting and was revealed to not be the issue.

•The fiber was checked with a simple laser to ensure we could see light on both ends of the cable.

•I do not need to switch RX/TX on the fiber, as this is a Yellow, Single Mode with a Simplex LC connector at each end.

How do I get the SG-300's to "light the torch" again?

•I've ensured that no copper is in the "shared" combo port (even if it was, the manual states the fiber should take precedence).

•I've tried rebooting both devices.

•I've tried inserting the SFP with the fiber already inserted

•I've tried inserting the SFP then the fiber,

•I've tried disabling and re-enabling the port's administrative status.
•Administration > Diagnostics > Optical Module Status on BOTH switches just shows "N/A" across the board.

Operational status still shows DOWN, and, again, the issue we experienced ended up having nothing to do with those ports, so why would known good SFPs and wiring suddenly stop working just because they were briefly taken offline?