Here are the console messages when the problem occurs. I will define the problem once again:
When clicking the download button on Mohave from the App Store, the App Store popup displays the following error message:
macOS Mojave failed to download
Use the Purchased page to try again.
Mohave does not appear on the Purchased page.
Please only reply if you know the cause and solution to this specific problem. Please do not attempt to supply a workaround.
2026-09-27 15:58:25-06 vangogh softwareupdated[470]: SUScan: Scan for client pid 470 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Failed Software Update - Refusing invalid certificate from host: swscan.apple.com
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Failed Software Update - Refusing invalid certificate from host: swscan.apple.com
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: SUScan: Elapsed scan time = 0.1
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: SUScan: Error encountered in scan: Error Domain=NSURLErrorDomain Code=-1012 "(null)" UserInfo={NSErrorFailingURLStringKey=https://swscan.apple.com/content/catalogs/others/index-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog, NSErrorFailingURLKey=https://swscan.apple.com/content/catalogs/others/index-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog, NSLocalizedRecoverySuggestion=Make sure you’re connected to the Internet, and then try again., SUErrorRelatedCode=SUErrorCodeScanCatalogNotFound}
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Scan got error The operation couldn’t be completed. (NSURLErrorDomain error -1012.)
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: SUScan: Scan for client pid 470 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Failed Software Update - Refusing invalid certificate from host: swscan.apple.com
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Failed Software Update - Refusing invalid certificate from host: swscan.apple.com
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: SUScan: Elapsed scan time = 0.1
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: SUScan: Error encountered in scan: Error Domain=NSURLErrorDomain Code=-1012 "(null)" UserInfo={NSErrorFailingURLStringKey=https://swscan.apple.com/content/catalogs/others/index-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog, NSErrorFailingURLKey=https://swscan.apple.com/content/catalogs/others/index-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog, NSLocalizedRecoverySuggestion=Make sure you’re connected to the Internet, and then try again., SUErrorRelatedCode=SUErrorCodeScanCatalogNotFound}
2026-09-27 15:58:26-06 vangogh softwareupdated[470]: Scan got error The operation couldn’t be completed. (NSURLErrorDomain error -1012.)