Delays happen. I'd say the statement below could fuel some conspiracy theories though. A batch of votes came out of Philly that didn't have one vote for Trump. From Aaron Bycoffe at fivethirtyeight:
And just as I wrote that, two more batches of Pennsylvania vote were reported: 23,277 votes in Philadelphia, all for Biden, and about 5,300 votes in Luzerne County, nearly 4,000 of which were for Biden. Trump’s lead in the state is now just below 6 points, with 83 percent of the expected vote in.