Hmm, that’s unusual… I’ve actually never seen that before. Could you send me some pictures from the inside of the cockpit, and maybe take one or two shots through the valve opening so I can see where tubes 4L and 4R are attached to the floor (if possible)? It does look like something might be separating there, but I can’t tell why. Can you see if the TPU is separating from the woven fabric, or if the TPU layers are coming apart like they weren’t fully welded? Just throwing out a hypothesis, if you focused on those areas a lot, maybe the excessive ironing broke the bond between the TPU and the woven fabric? If that’s the case, adding a line of stitching with a heavy-duty needle and thread might be the best fix, and/or gluing with something like Clifton LA 4123 Urethane Adhesive.
If you’re using a pump to inflate it, be careful not to put much more pressure into the packraft than you can do by mouth, because that could be part of the problem.