Hmm... very odd. On our end, I'm seeing a non-null constraint error involving the template_id column coming from your org:
insert into "input" ("events") values ($1) returning * - null value in column "template_id" of relation "input" violates not-null constraint
I'm not sure that explains the behavior you're seeing in the UI but it may be worth investigating the values you have in that column. Also would be curious to see if any errors or failed requests are showing up in your browser's dev tools when making the UI edit.