OK, I give up with the @pixelfed #Instagram archive #import.
It sometimes breaks and only imports X photos, but other photos I had selected are no longer available for selection, because it somehow thinks it's imported them too. No idea where and why it fails, and I think it will be easier for my sanity to manually import them into #Pixelfed, even if this doesn't keep their original dates.
Great feature to have though, I did import many photos. Just don't know which ones didn't make it...