Address the Biden bump in these specific districts and why it occurred.
Easy Peasey!
The absentee votes were counted last, after the electronic election day and early votes were counted...
Trump encouraged his voters, to vote in person, regardless of COVID19 spreading.
Democrats encouraged their voters to stay safe, and vote via absentee ballot.
For months ahead of the election, it was reported, from every news outlet, that the absentee votes in the swing states were not able under their laws to be counted prior to election day. This law, preventing the counting of absentee ballots as they came in, was put in by the mostly Republican majority legislatures in the swing states. Democrats sued to change it and start earlier like most other states did, but lost in court. They reported that on election night, it would appear Trump could appear to be winning, because most Democrats would be absentee voters and those would not be counted until way later in the nght, the wee hours of the morning, and likely through the next few days, because there were so many absentee voters this year.
The process of counting absentee ballots is tedious and longer. First the envelopes have checks.... that signature match, a legal registered voter, who also requested a ballot, some states also require address and other requirements, have been done or are done.
And once that process of checking the envelopes is done, the envelopes are opened, then the ballots removed, then the ballots unfolded and flattened so they can flow easily it in to the scanner, then stacked in batches... and put in to suit cases that are called ballot cases, and stored until the workers responsible for feeding the batches in to the automated vote counting scanner, need them.
All of the processing takes much longer for absentee ballots.... Which were known to lean Democratic.
The rise in Democratic votes on election night, began when most of the same day votes had been counted already, which would have been Republican leaning, and the absentee batches of ballots were finally being counted by scanners.. In the wee hours of the morning....democratic leaning.... Just what your chart shows.
There was no anomaly with your chart, what it shows, is what was expected....R voters counted mostly early, D voters counted mostly later.