Have you closed all Zotero windows? When you click on the top-right cross of the main Zotero window (in Windows), it does not "Exit" Zotero, but only closes the main window. If you have other windows opened, like Preferences or PDF viewer windows, they will stay open even after clicking the top-right cross of the main Zotero window. If you want to really close all Zotero windows, you need to go to File -> Exit.
I have faced a similar situation before, so I just mention it here in case it is a similar situation for you. I was a bit confused, as I was expecting the "Exit" behaviour when clicking on the cross. I missed the other windows left opened because they were on another monitor. This is similar to the behaviour of Firefox with multiple windows. I am not sure though why this would be useful in Zotero, as after closing the main Zotero window, I could not find any way to reopen it from the windows left opened. The File -> Show in Library menu option does not do anything. So it seems to leave only a partially functioning software.
If it is not the case for you, it would be useful to provide more information on the problem you are experiencing.
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When you click on the top-right cross of the main Zotero window (in Windows), it does not "Exit" Zotero, but only closes the main window. If you have other windows opened, like Preferences or PDF viewer windows, they will stay open even after clicking the top-right cross of the main Zotero window. If you want to really close all Zotero windows, you need to go to File -> Exit.
I have faced a similar situation before, so I just mention it here in case it is a similar situation for you. I was a bit confused, as I was expecting the "Exit" behaviour when clicking on the cross. I missed the other windows left opened because they were on another monitor. This is similar to the behaviour of Firefox with multiple windows. I am not sure though why this would be useful in Zotero, as after closing the main Zotero window, I could not find any way to reopen it from the windows left opened. The File -> Show in Library menu option does not do anything. So it seems to leave only a partially functioning software.
If it is not the case for you, it would be useful to provide more information on the problem you are experiencing.
occasionally happens since probably 6.0.10
close the main window, but the process is still there