Uploading Chunk 1/12 [==================================================] 100% [035305] The following tasks did not complete: theme:deploy, startDeploy [035305] Did you forget to signal async completion?

Yeah, it does that a lot. It's better than it used to be. Just keep trying until it works.

looks like I was having intermittent network connection issues.

Maybe, maybe not. Sometimes it helps to close other things that use the network, like messaging apps etc.