I have a really weird issue with a certain model of Cisco switches. The industrial IE2000 models come with a SD card slot, which can be used to store the configuration or boot from. I had 5 of these switches to commission and they are in a quite industrial setting so I figured I'd configure one of them at my desk, copy the config to the SD card, swap the SD card and do the changes needed for the next switch and swap the SD card, etc. etc.
I did exactly that, resulting in 5 SD cards with identical configurations except for the hostname and IP addresses.
When I went to install the SD cards and copying the config from SD-card to the onboard flash, everything worked just as expected, except the SFP ports.
The ports all complained about Low TX Power Alarm (they were fitted with GLC-FE-100LX modules), and correctly, the TX power was low on every fiber port.
I couldn't find anything wrong with the config or the modules, so I did a factory reset, and typed in the config manually this time. And then it worked. Every single time, in 5 identical switches with almost identical configs. I even compared the config I had on the SD cards to the one I typed in, and I can't find a single difference between them.
Has anybody else ever seen anything like this? Is there some command that has to be issued to make the fiber modules actually send signal out? Or some command that disables that? The modules could detect signal coming from the far end switch, and I verified the measurements in the switch with an optical power meter.