After creating a new package of my managed product I have encountered an issue where this package cannot be installed in many customer environments. This package was created in a Winter 17 environment therefore cannot be installed in an environment with a lower Salesforce release version.
After contacting Salesforce, they notified me that this issue is considered as their "blackout period" and the behaviour I am seeing is referred to as "working as designed".
I took notice that your packaging org is on our Winter '17 release. As the affected org is on Summer '16, this behavior is considered "working as designed". A package cannot be installed in an org where the packaging org is on a newer release. This is called our "blackout period". The affected org will have to wait until it is updated to Winter'17 for your package to install. Here is a link to where you can see the release schedule, click on the instance number and look for a circled date and for "Winter 17 Major Release".
Looks like some of my customers cannot get the latest version of my product until Salesforce have rolled Winter 17 onto their instance.