Dont modify a list as you are traversing it. The result is

implementation dependant although with CPython elements are
unintentionally skipped during iteration.

Basic CPython example:

>>> A = [1,2,3,4,5,6]
>>> for a in A:
...     A.remove(a)
>>> A
[2, 4, 6]

jellyfin_kodi/library.py

@@ -131,11 +131,10 @@ class Library(threading.Thread):
             Start new "daemon threads" to process library updates.
             (actual daemon thread is not supported in Kodi)
         '''
-        for threads in (self.download_threads, self.writer_threads['updated'],
-                        self.writer_threads['userdata'], self.writer_threads['removed']):
-            for thread in threads:
-                if thread.is_done:
-                    threads.remove(thread)
+        self.download_threads = [thread for thread in self.download_threads if not thread.is_done]
+        self.writer_threads['updated'] = [thread for thread in self.writer_threads['updated'] if not thread.is_done]
+        self.writer_threads['userdata'] = [thread for thread in self.writer_threads['userdata'] if not thread.is_done]
+        self.writer_threads['removed'] = [thread for thread in self.writer_threads['removed'] if not thread.is_done]
 
         if not self.player.isPlayingVideo() or settings('syncDuringPlay.bool') or xbmc.getCondVisibility('VideoPlayer.Content(livetv)'):
 

jellyfin_kodi/objects/kodi/artwork.py

@@ -147,9 +147,7 @@ class Artwork(object):
 
     def add_worker(self):
 
-        for thread in self.threads:
-            if thread.is_done:
-                self.threads.remove(thread)
+        self.threads = [thread for thread in self.threads if not thread.is_done]
 
         if self.queue.qsize() and len(self.threads) < 2: