I re-installed 2.7.13 Pro and I no longer see lots of Dropped I/O (Input probs, actually). Instead, I'm apparently seeing a very short-term representation of the I/O because it rapidly jumps between 0% 33% 50% 66% and 100%. So, maybe 2.8.5 was simply giving an accurate long-term statistic, one which I hadn't expected because the short-term stat often shows 0%.

re uploads, I'd noticed that no one was getting past 0% 1% or 2%, even though the upload speeds were good. Could it be that 2.8.5 is miscalculating the percent-uploaded only as a short-term stat, based on the chunk-size vs the entire file-size? That certainly seems consistent. Now that I'm back on 2.7.13 Pro, I'm seeing uploads at a "normal" range of completed percentages again. Since they're probably the same people who were uploading from me before I cut them off, it would certainly indicate that 2.8.5 was simply misreporting them.