First thing I try when inserter are acting strange, is removing and replacing them. They sometime just bug (mostly in MP). Have you already try that ?
Thanks, that did the trick, working now.

if they are flashing no fuel it means that they are fully out of energy and cannot do anything (even ...

Well, it didn't take long to stop working again, this time the belts are full, the solid fuel is not moving and some burner inserters can't pick up fuel. So what now? Any ideas?

Yes, you were right. I downgraded the belts and it worked again. Thanks

After playing with this setup for hours, it suddenly stopped working. Most of the inserters just won't grab the solid fuel, some do. Can somebody tell me what I'm doing wrong? Or is it a bug? (fyi: the inserters that won't grab the solid fuel move slowly like if its broken or something)