Hi,
This does not appear to be a breakpoint issue. The row contains two equal-width columns, so hiding the empty column does not necessarily make the content column expand automatically.
Edit the row/columns and:
Hide the empty column on both Tablet Landscape and Tablet Portrait.
Set the content column width to 100% on tablet, or enable Fill Columns for the tablet views in the Row settings. SP Page Builder controls column visibility and column width separately.
Clear the Joomla, template, and browser cache after saving.
The blank area you are seeing is most likely the first column retaining its original 50% width, rather than the hidden column still being displayed.