Hi,
Thank you for testing this across both iOS and Android and confirming that image expansion still works on desktop.
As the forum’s AI answer recommended, comparing a minimal hosted-content image with an otherwise identical HTTPS image is a useful next step. However, I would clarify a few points before treating this as a confirmed regression.
Microsoft’s Teams documentation states that tapping an Adaptive Card image should open it in Stageview on mobile, even when the allowExpand attribute is absent. The same documentation still includes the "msTeams": {"allowExpand": true} image configuration you are using. Therefore, your symptoms do not establish that this property has been removed or that you need to replace it with a top-level image property.
Reference: Format cards in Teams — Stageview for images in Adaptive Cards
Also, the current Teams card reference lists mobile support up to Adaptive Card version 1.6. The AI answer’s statement that mobile support stops at 1.5 needs correcting. Since you have already tested versions 1.2 through 1.6, repeating schema-version changes is unlikely to help isolate this issue.
Reference: Types of cards — Support for Adaptive Cards
For the comparison test, keep your existing msTeams configuration and change only the image source. Use a non-sensitive HTTPS test image that renders successfully on mobile. If that image expands but the hosted-content image does not, it would narrow the investigation to the hosted-content path. It would not, by itself, confirm the underlying cause.
The suggested Action.OpenUrl button is a reasonable temporary workaround to test, using a file link that affected users can already open. Microsoft Graph’s messaging documentation supports this action for card attachments. However, do not use ../hostedContents/1/$value as the button’s URL: use an actual user-accessible HTTPS file link. A Graph hosted-content endpoint requires authenticated API access and should not be assumed to work as a browser link.
References:
The behavior you describe suggests a possible Teams mobile issue, but confirmation requires investigation. As the AI answer recommended, ask your Microsoft 365 administrator to open a support case with the exact Teams builds, a sanitized minimal request, and the hosted-content versus HTTPS test results.
Could you share the exact iOS and Android Teams versions and the minimal card JSON, with sensitive information removed? Those details would help distinguish an issue specific to hosted images from a broader mobile Stageview problem.