I have opened a support case in August following your post. FTNT reported back that there might be a compatibility issue of the memory modules employed. As I suggested a BIOS upgrade the supporter stated that they have already included a fix into the next firmware (v5.2.4). As my customer (and me) didn't agree to update he sent me a special build based on v5.0.12 (build 8408 instead of b305).
After installing and now 35 days uptime everything looks OK. But then again, what is 35 days compared to the usual 100+ days it took to run the 600C against the wall in the past. I will have to watch and wait to see if the fix really is working. Meanwhile, maybe it's worth asking support for the special build and see if that helps in your situation.
As already mentioned earlier, this is a known issue (bug :0243461) and there is a special build released in both V5.0 and V5.2.
Also, there is a workaround of bringing DOWN the admin status of all the UNUSED interfaces should prevent the issue to re-occur.
Hope that helps.
Well, all is not well, even with a relatively new 600C from Fortinet with a recent firmware.
Has anyone had this issue resolved yet?
At this point, it appears that there is a serious bug in the 600C firmware with no real resolution.
The earlier-mentioned Reddit posting made it seem like there were other models that were affected, so I am curious if there are other Fortigates in the C hardware revision that also have this issue.
If someone has some wisdom to share on this, please feel free to jump in.