Debugging a simple single-mode fiber connection problem

After lots of experience with wired and wireless networks, I've recently started to play with some basic fiber equipment. To that end I've purchased some single-mode fiber cable (#40203), SFP transcievers (#75327) and gigabit ethernet media converters (#35333) from fs.com

Using the basic default DIP switch configuration (all OFF) I am able to get two devices with static IPs connected with a stable connection between them. I can even run an iperf bandwidth test with good results (capped at 1Gig NICs on both sides).

However, if I try to connect something like this scenario:

laptop <UTP> converter <fiber> converter <UTP> home router

Then I initially get a ping, a DHCP allocation, and a connection, and all is good. But after a few seconds of real world network usage, the fiber loses connection (can be seen by the fiber link LED going off) and never comes back unless I power cycle both the media converters.

This is pretty weird behavior that I'm not expecting. Am I doing something wrong? Any ideas?

Edit: I'm doing some testing now with Link Fault Passthrough (LFP) turned on and it seems to be a bit more stable, but stll after a few mines I get the same disconnects