Perhaps not 100% a bug but definitely undesired behaviour:  When a city cannot construct the current item at the front of the queue, it silently stops construction, and the whole queue fails to process.

Desired behaviour: When a city cannot build the constructable at the front of its queue, it should work on the next item instead (Endless Legend does this)

Steps to reproduce:

• Block a city's spawn point with a full army and attempt to build more units.  The army cannot receive  additional units, so the city will not produce units... but it won't tell you it's stopped being productive or move on.
• Build infrastructure that requires a strategic resource (for example, Animal Barns or Forge) and then pillage your empire's only source of that resource.  Construction will stop, but the city won't tell you it's stopped being productive or move on.