I was having this issue connecting to the Jypter notebook on my Ultra96 PYNQ system after imaging a new SD card. Luckily, a colleague pointed me to this solution:
https://github.com/Xilinx/PYNQ/issues/851
Turns out it related to an outdated clock setting on the board when Ultra96 hasn't gotten its clock updated yet. Update the system clock and problem is solved!
Best Regards,
-Kevin
P.S. Thank you Fred K for saving my bacon on this one!
