In the ArcGIS Field Maps mobile app, a field configured with a conditional visibility becomes blank once the attribute value in the previous question is reverted.
This issue is not reproducible in ArcGIS Field Maps when utilizing the 'Preserve values when fields are hidden with conditional visibility rules' setting in the Form Settings.
ArcGIS Field Maps documentation: https://doc.arcgis.com/en/field-maps/latest/prepare-maps/configure-the-form.htm#ESRI_SECTION2_33905D7FB83F450A91168A5DD0FBA62E