I don't know if my experience could help you, but it seems that the DATA quantity which is possible to store into a Mobile Lab is hard capped. I remember being something like 621/750 and transferred an experiment worth 162 data into the lab, the experiment disappeared but no DATA was stored into the lab (number was still stuck at 621).
Reloaded an earlier save and resolved by using Kerbal Alarm Clock multiple times to transmit when near Science cap in order to consume enough DATA allocation.
Not sure if bug or intended, but be mindful of DATA size of your experiments before transferring them to a lab (at least in my experience)
