Problem: I made a foundry-mission pre season 8 and haven't really played since then. Now I wanted to share this mission with a friend and he cound not find it ingame. Here are the published informations:
Hmm, wasn't there a bug related non-English missions not showing up properly in the search? Try temporarily setting the language to English and see if it shows up then.
He published his mission in German, which means he could only find this mission when the German language has been selected in the mission/foundry search screen. It usually defaults to English instead (and therefor your mission couldn't be found).