Good that we have this forum to report and discuss issues. Maybe I can even fix some of them.
1. An error message box is usually shown on crash. Moreover at least a one line error message should be written into log. Have you checked the log-file? Much more useful info can be collected with debug build - please see https://nzbget.net/crash-dump
. If the process just terminates - could it be that some other program is doing this? That'd be strange though but who knows. Anyway with debug build and crash dump this can be catched.
2. Looks like the second program instance (launched via desktop icon) isn't communicating properly with the first instance. To figure out what is happening I need to build a special version with more logging in related code. I would send you such version to try if you are willing to help with debugging this.
4. When that happens, please refresh the browser page or close the page and open. Does this change anything? What I'm trying to find out with this: is webui not updating or the queue items are stuck. If queue is stuck then creating a memory dump of the running process can be extremely helpful to me. Please see the link for crash dumps above.
5. If the program crashes often, some files indeed can be left because the program state may not be saved properly.
About "missing" features. Whether some feature is desperately needed or a ballast depends on ones point of view and personal needs.
1. There is a solution as you know already. If you don't want to install Python that's not a good excuse. There are many useful scripts. I can't embed them all and that would be against the idea of users extending the program. You should install Python, you might find other scripts useful too. One day you might write your own script to automate something that no one but you needs.
2. Free space is not such important information to be put on front page. Again, this is a personal opinion. Moreover this also a design thing and in no way a lacking feature. BTW, if you constantly have disk space issues you probably need a larger disk.
3. Predicting completion time is not possible because post-processing time can not be estimated: repair, unpack, executing scripts - that can take any amount of time.