https://www.americanghostwalks.com/articles/1897-milwaukee-a...
https://www.wildquincy.com/blog/1897-quincy-mystery-airship-...
https://www.audacy.com/podcasts/dark-histories-49725/phantom...
Then on the other hand I find the classic “they wouldn’t have been able to understand what they saw” theory unlikely because an airship made of shiny metal or something else would have been distinguishable.
EDIT: After reading a bunch of contemporary accounts I am starting to think most of these stories are talking about dirigibles. There was evidently a lot of work going on internationally to get men up in the air and flying under their own control. Several accounts suggest that it would be a useful military tool that would be more flexible than tethered balloons. Since Langley at the Smithsonian actually demonstrated a steam-powered model contraption that won him a Navy contract in about 1896 and resulted in several failed flights including one only 8 days before the Wright brothers flight in 1903, it is obvious that a lot of effort was being expended on mastering powered flight at the end of the 19th century.
Evidently not all of the inventors were interested in the enormous profits that one could earn as one article in a California paper noted after interviewing the lawyer supposed to be associated with the inventor of the airship observed in those 1896-1897 sightings. That article's author said "So far as the public is concerned the inventor does not ask any one to invest in the enterprise. Perhaps this may be evidence of insanity. I will admit that this is the first time to my knowledge that anybody had anything in California in which he did not want anybody to invest money." [0 - Hart's inventor has three aerial fliers.] LOL. Some things never change I guess.
[0] https://chroniclingamerica.loc.gov/lccn/sn85066387/1896-11-2...