Users attempting to update from SnapGene 5.2.1 on macOS may see an error dialog if SnapGene automatically checks for updates, or when they click menu SnapGene → Check for Updates:
"Sorry! An issue with the software update mechanism means you must download and install the latest version manually."
If you see this message then click the download and install link in the dialog to manually download the latest SnapGene installer disk image (.dmg).
Quit SnapGene, then open the .dmg file and copy SnapGene to your Applications folder. Choose to overwrite the existing SnapGene installation.