It just fucking deleted my recipe whilst I was in the process of brewing it

I was using the app and the desktop simultaneously to brew a beer. I've just about finished it and was putting some data into the app. I go back onto the app to check it and it's disappeared. I get some sort of bullshit javascript error. Then I go back to the desktop to add the data there and it's also missing from there.

What the fuck?

I'm assuming that you've looked at the cloud for it?

BeerSmith is not synced or networked in a way that protects data. It works as flat files. Either device can modify the file, overwriting the other. The second device can see that as a corruption, causing an error and sometimes deletion.

On the desktop version, go to the archive and find the most recent "edit" version of your recipe. You can restore from that.