What’s the most challenging bug you’ve ever encountered, and how did you solve it?

I'll start!

This bug is something of a quirky little thing inside Invision Board Forums. I use Zapier to bring in some Blogs/Articles, etc. One of the fields that can be pulled in is the IP address of the article's creator, or blog it came from. Sometimes this will be the Author's Name, or Website it came from instead of an IP address.

Now, why I call this a bug, is because Zapier will produce a 500 error and say the ZAP failed. But actually, it didn't. The article still loaded, and the IP address is whatever was put in there. Since this is a 3rd party application, and version 5 will be coming out soon. I just ignore the IP Address field, and it resolves correctly.