Cannot create output

I was just updating my outputs. I would create a new/temp one, test that its results were as expected, then update an existing one and delete the new/temp one. I did this a few times no problem, then suddenly when attempting to add a new output I only see a yellow cancel button. No green save button.

Status says free heap is around 20,000. I have 3 integrators configured and 12 outputs.

Is this a resource issue? The only thing that has changed since the last time I successfully created a new/temp output another output is now using an integrator in its script.

Does referencing an integrator in a script use more resources than referencing an input? Or is it just the existence of the integrator itself (regardless of any usages in outputs) that is resource intensive?

Update: it seems to be the length of the output name. self_consumption_2 is too long, but self_consumption (already existing) is OK?