Dynamic batching is behaving odd

People, I am confused.
What does it mean in the frame debugger when you get unexpected extra events without an explanation as to why dynamic batching didn't mop them up?

As you can see from the image I have some straggler models not being drawn with the rest and it doesn't provide any info. They all share the same material but none of them offer a reason why they aren't batched.

Should I interpret this as an indication that a batch reached it's maximum combined size? My scene is 5k vertices total shouldn't it fit into one batch? If the scene didn't fit into one batch shouldn't the rest be drawn in the second batch instead of being drawn separately, or does batching stop after the first batch is filled?

What is quite strange is that I have 3 materials - a material for vertex-lit meshes, a material for unlit particles and a material for transparent effects. And they seem to batch together which makes no sense according to documentation. Shouldn't this break batching?

 

I'm on 2018.3.
From my observations there are specific cases where if objects happen to align well everything batches together. Literally the frame debugger shows the entire scene(excluding post processing) with particles and transparent objects being rendered in the clear event. But most times some meshes end up left out of the batch. There might be good reasons for it, I just want to understand the system better.

I still haven't got a clue how batching manages to draw transparent effects and opaque geometry at once. Or maybe it doesn't, but it makes it look that way?