What is transaction not found on blockchain mean? Does that mean transaction still waiting in mempool, unconfirmed or never broadcasted on blockchain?
Is this waiting in miner's mempool to be picked up? 
  


No. Broadcasted transactions are visible on block-explorer sites (in most cases)


  
  Is this unconfirmed and already dropped from the blockchain network. 
  


It is unconfirmed, but not because already dropped, but because not yet broadcasted


  
  Transaction have some error to start with and never broadcasted on blockchain network? 
  


May be. Only sender knows the correct answer


  
  None of the above and have some other issue?
  


If it is not seen - it does not exist. Point.