I just received an email from Lacerte that there is a new update available to fix the problem (see note below).  May it be a good fix and I wish everyone many happy (tax) returns! 🙂 

"2020 Slip Sheets - Landscape Return Mailing Slip Sheets Misaligned After Update
This unexpected behavior has been addressed in a program update available October 13, 2021 (Version 41.1013)"