In some of my tests I noticed it being an issue of the Testnet Latency. We were using dev.cryptolions.com:28888 instead of a monstereos dedicated full node. And to create a transaction eosjs does some actions like get the current block, validate the abi parameters etc. so it's like 2/3 requests before the popup comes out.
RE: MonsterEOS: Creating your First Monster in EOS Jungle Testnet