I was having very similar issues as the original post. I received my 4 cells at about 3.29V each and after 4 days charging in parallel, was only able to achieve about 3.34V using a regulated power supply. I even bumped the voltage up to 3.7 to get is closer to 5-6A output.
I finally built the battery in serial and after about 8 hours @ 14.1V and 10A, I managed to get them to about 3.38V. But now my Overkill BMS is saying they are at 99% of the 280AH capacity with just 3.38V/cell. I was expecting them to be well over 3.5V/cell at this capacity?
I did not that my PS seemed finicky - moving the wires caused big deviations in Amp output. I switched to eyelet connectors and that helped a little. However, this capacity and V thing is concerning me. I plan to hit 100% on the BMS, then go back to parallel top balancing to try and achieve the ~3.6V/cell upper limit. Or should I be happy with the ~3.4V/cell I appear to be able to achieve at 280AH capacitance?