The application during installation reports that "the package file is signed incorrectly"

Question

Java

I have two apps on google play. Each is signed with its own key. Users report the error that I wrote in the title.
Signed apk files with the same key. Can't upload to google play. Says that it is necessary that all apk files of one application must be signed the same way.
What to do? This message occurs spontaneously. On one device, both applications are installed normally, on the other, only one of them is installed. The one that was installed first is installed.