A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hello Haseeb Akhtar,
We appreciate you spent time doing test and sharing the result with us. So the simple HTML page doesn't work on mobile phone neither.
We deeply understand the issue has affected your daily work. Apologize for the inconvenience. We know how hard it is when things do not go as expected.
On your mobile phone, you may also try to use a different browser (such as Chrome) to access the test HTML page and the third-party website to check the outcome. This way helps you narrow down whether the issue only happens in a specific browser on mobile phone.
If same issue persists in different browsers, we do understand the frustration and feel very sorry about it. We also notice it looks like an urgent issue. Since we cannot reproduce the issue from our side, it may need to further check your tenant and check the issue from back end for further investigation.
In this situation, we sincerely recommend you inform your Microsoft 365 admin of the issue and help you create a support ticket via Microsoft 365 Admin Center.
The support team there has higher permission to check the issue further and the correct escalation channel for this case. This is also the most efficient way in handling this kind of issue for you. For reference: How do I find my Microsoft 365 admin Get support | Microsoft Docs
Thanks for your patience and understanding so far. Hope you are keeping safe and well!
Best Regards,
Tina