The bar rests in the first bar of B, ie the bar before the empty bars, are explicit rests with the Ends voice property set. You can see this by showing rest colors.
Select those bar rests and press Delete to turn them into implicit rests. The bar rests in the following bar should reappear, because the Ends voice property can’t be set on implicit rests.
In general, missing rests or very narrowly spaced bars (like in the part) will be a result of rests being suppressed somewhere, somehow. Showing rest colors and looking for the Starts/Ends voice properties are how you can identify what’s causing that in future.