Error Log:
609.489 Error MainLoop.cpp:1223: Exception at tick 1021539: The mod Burner Leech caused a non-recoverable error.
Please report this error to the mod author.
Error while running event Burner-Leech::on_nth_tick(1)
Entity is not inserter.
stack traceback:
Burner-Leech/control.lua:102: in function 'leech'
Burner-Leech/control.lua:85: in function <Burner-Leech/control.lua:52>
stack traceback:
[C]: in function 'index'
__Burner-Leech/control.lua:102: in function 'leech'
Burner-Leech/control.lua:85: in function <Burner-Leech/control.lua:52
609.489 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Burner Leech caused a non-recoverable error.
Please report this error to the mod author.
Error while running event Burner-Leech::on_nth_tick(1)
Entity is not inserter.
stack traceback:
Burner-Leech/control.lua:102: in function 'leech'
Burner-Leech/control.lua:85: in function <Burner-Leech/control.lua:52>
stack traceback:
[C]: in function 'index'
__Burner-Leech/control.lua:102: in function 'leech'
Burner-Leech/control.lua:85: in function <Burner-Leech/control.lua:52>
609.489 Info ServerMultiplayerManager.cpp:776: updateTick(1021539) changing state from(InGame) to(Failed)
609.489 Quitting: multiplayer error.

Entity is not inserter.
Well... there's the problem :|

I assume you have other mods that are active?

Though, I've added an extra check to make sure that the entity is in fact a burner inserter at time of leeching.
If this crashes again, could you please provide a save file?

have put the updated mod version on the server and we'll shout if anything goes bang :)

So the error happened on the latest version. Error:
2920.953 Error MainLoop.cpp:1223: Exception at tick 4835259: The mod Burner Leech caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Burner-Leech::on_nth_tick(1)
Entity is not inserter.
stack traceback:
Burner-Leech/control.lua:109: in function 'leech'
Burner-Leech/control.lua:92: in function <Burner-Leech/control.lua:52>
stack traceback:
[C]: in function 'index'
__Burner-Leech/control.lua:109: in function 'leech'
Burner-Leech/control.lua:92: in function <Burner-Leech/control.lua:52

It occured during this screenshot stage (low resolution soz). There is fire and death inside the base where the inserters are.
https://steamuserimages-a.akamaihd.net/ugc/781857270463772442/CAA084297EE2515E48AE6FDBB2E255C7DEB03F62/?imw=512&imh=288&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=true

In the error its line 92 that's calling the Leech() function. But there isn't an entity type check on line 83 and so I think a fire or flame entity is getting created on the exact same spot as the inserter died at and then this flame entity is being passed in to the Leech() function.

Ah.
Thanks for the report.
I'll get that extra check in for the next release.

This should be resolved in 1.0.4.
I added a check to the find_entities_filtered to only look for inserters.