Distributing iOS with profiles, without third party authentication for the end user

Question

My company has an enterprise apple license, and I want to distribute our app to the employees. For this we use appcenter with a public url to download the app. Earlier this worked flawless, they could download the app and easily go to profile settings on the iphone to install the required profile.

Now this doesn't work anymore and I have no idea why. The app can be downloaded using the same url, but when trying to open the app the error message "Unable to Install, This app cannot be installed because its integrity could not be verified". And In the VPN & Device Management, there is no new profile to be installed.

Being logged in and authenticated to appcenter, then I can download the profile from there by tapping +Device. But I don't want all the employees to have an AppCenter account.

Is there a way to get the appcenter app profile without an appcenter account, as was possible before? Or another way to distribute this without having all employees to set up a third party account somewhere?

I tried to distribute my public app using public appcenter url and expected my employees to be able to install the app without the need of an appcenter account.