When you copy all the cells in a large row, move to another table, and try to paste, you lose much of the data. In this gif, I’m copying a long row and pasting it into a new table:
Very likely you’ve went over size limit for these operations… If you open the console you may see some error messages.
I’ve had a few docs crashing over related issues, not sure what we can do at this point except wait for a better algorithm from the devs.