I've had a custom button for several years which opens a Zoho Form and populates it with data.  This was ideal for mobile users, who used it to capture signatures and complete CRM Cases while in the field. 

This stopped working mid-May, the bug was reported and acknowledged but is still not resolved. 

This applies to opening a URL from with the CRM mobile App using the "In-App Browser"

Just in case anyone else is having the same issue!