The most likely scenario based on all the reports I've read is a variable altitude balloon (similar to Google Loon). The second most likely is a hybrid airship

The most likely scenario based on all the reports I've read is a variable altitude balloon (similar to Google Loon). The second most likely is a hybrid airship. https://en.wikipedia.org/wiki/Hybrid_airship https://en.wikipedia.org/wiki/Hybrid_airship