Cannot open .acsm files from Google Play Books

I'm getting the following error in Adobe Digital Editions (v4.5.12.85) on Mac every time I try to open .acsm files purchased from Google Play Books:

"Unable to download. Error getting License. License Server Communication Problem: E_ADEPT_XML_SYNTAX"

Solutions I've already tried:

• Deauthorized (Ctrl+Shift+D) and reauthorized with my Adobe ID
• Deleted all ADE data from ~/Library/Application Support/Adobe/Digital Editions/
• Completely uninstalled and reinstalled ADE (clean install)
• Reauthorized with the same Adobe ID used for the purchases
• Downloaded fresh .acsm files after reinstalling

None of these steps made any difference. Same error every time.

I also contacted Google Play support first, and they said this is an Adobe-side issue. Then I contacted Adobe support directly, but was told ADE doesn't have support and was directed here.

Has anyone been able to resolve this? Any help would be greatly appreciated. I just want to read the books I paid for.

Thank you.