The ALMA Observatory circulated a report of issues affecting mosaic images produced with CASA in ALMA Cycles 1-5.
Over the course of the last several months an issue in CASA mosaic imaging was recognized. The Observatory elected to understand and characterize the issue before informing the user community of potential impacts on the resulting images. The CASA team has now identified a couple of issues using both the 7-m and 12-m arrays over the course of the past few cycles and CASA releases. The full extent of the data affected is still being investigated.
You can read further details on the identified issues in this link to the Science Portal.