A few more ideas in case you have not tried these:
For completely inscrutable errors you may want to build a minimal app with just the stuff necessary to break things. i.e. start with what you have now, in a new folder/repo, strip away pieces bit by bit, until you either a) can’t strip it down any more or else you don’t get the problem any more or b) understand what’s actually going on.
Usually it’s high complexity that keeps us from seeing what’s actually going on and might be breaking.
Now, it may also be an actual problem in a library or Meteor itself etc. In that case you’d need to up your debugging tools game, e.g. bring in a network proxy/sniffer (can’t recommend one), begin debugging the code being executed from start to finish. You have the whole source of all packages involved available so it’s possible.
It’s usually almost impossible to spend more than a few hours on a single problem without progress, except if completely sticking around in confusion, stumbling in the dark. If that happens be sure to step away before such an incident eats a whole week or more…
And a few questions:
Does “local” mean using just
meteor to run the app? What deployment process / env do you use for “online”?
There’s one weird bug that if you use nginx on Mac OS (in front of the app, or in front of anything, really) and have the sendfile option on it also gives you all kinds of weird errors; but your description doesn’t sound like this would be a good explanation for the observed behavior.
Also: Put your images on Dropbox, make them public and share the links here. Or use another image hosting service (even imgur works for this I think).