Not at all. PushLink is fully under a try/catch Throwable block.
Until version 5.0.4 it uses two ports. Https 443 and Tcp 6670. Check if they are opened in the firewall. In version 5.1.0 or higher it uses only the 443 port. (That's very good!)
Two permanent threads. One to listen for the push notification. Another to send heartbeats to the server. Both are lightweight. Eventually, a third thread is opened to perform the apk download.
Yes, it is. But you have to do some tests with the combination "device model" + "OS version".
Maybe your device clock is too late or ahead.
Maybe you forgot to call PushLink.setCurrentActivity when using popup strategies.
You are starting PushLink inside your own thread. Start it inside the main UI thread.
Installation means a single linux/android process using PushLink. If one device runs two applications using PushLink, there are two installations.
You have reached your plan limit and PushLink will register as disabled the new installations from now on. Disable means that you can see them on administration, but can't send updates or receive exceptions.