When destroying a Logistics Signal Player Request combinator I get the error below this message.
What's interesting is that this player request combinator is not showing any outputs even though I'm requesting from the logistics network.

Also, placing another one down and deleting it results in the same problem..

Error message:

The mod Logistic Signals (0.6.1142) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event logistic-signals::on_pre_player_mined_item (ID 11)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__logistic-signals/control.lua:27: in function <logistic-signals/control.lua:16>

factorio-current.log note:

9064.552 Script @logistic-signals/control.lua:34: onEntityDeleted called with an entity that was not tracked
9065.956 Info ClientSynchronizer.cpp:335: Latency changed to (12)
9080.176 Error MainLoop.cpp:1283: Exception at tick 107813951: The mod Logistic Signals (0.6.1142) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event logistic-signals::on_pre_player_mined_item (ID 11)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__logistic-signals/control.lua:27: in function <logistic-signals/control.lua:16>
9080.176 Error ClientMultiplayerManager.cpp:98: MultiplayerManager failed: "The mod Logistic Signals (0.6.1142) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event logistic-signals::on_pre_player_mined_item (ID 11)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__logistic-signals/control.lua:27: in function <logistic-signals/control.lua:16>"
9080.176 Info ClientMultiplayerManager.cpp:611: UpdateTick(107813951) changing state from(InGame) to(Failed)

That should not be possible to happen. I cannot explain this, it is actually checking that the entity is valid before accessing any other properties of it. The only possible explanation would be the game deleting entities while its running mod callbacks, which would be a flaw in the actual game code.

So, I report this to the game developers then?

It's inconsistent, but it does happen.

After checking again, I may have found the reason for this. Might be fixed with 0.7