Processing again step 3 should solve the problem.
The bug was happening either when clicking on Save or when clicking on Export.
If you clicked on Save then the corrupted tiles are not written on the disk and therefore when you click on Reset it solves the issue.
However, if you clicked on Export and got the error with a previous version of Pix4Dmapper, then the corrupted tiles are written on the disk and when you click on Reset with the version 2.0.80 it does not solve the issue because it is loading the corrupted tiles. In this case the only solution is to process again step 3.
Note that if you drew regions in the Mosaic Editor, processing again step 3 it will remove them and you will have to draw them again.