rqt_bag GUI does not display image messages

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My OS is Ubunutu 20.04 using ROS Noetic and python version Python 2.7.18 and graphic card Intel UHD Graphics 620. Given the bag file from https://open-source-webviz-ui.s3.amaz..., when I run "rqt_bag demo.bag" the gui is not displaying image messages (i.e no thumbnails on the timeline). In the terminal, I receive the following warning:

Exception in thread Thread-8:

Traceback (most recent call last):

File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner self.run()

File "/opt/ros/noetic/lib/python3/dist-packages/rqt_bag/index_cache_thread.py", line 67, in run updated |= (self.timeline._update_index_cache(topic) > 0)

File "/opt/ros/noetic/lib/python3/dist-packages/rqt_bag/timeline_frame.py", line 838, in _update_index_cache for entry in self.scene().get_entries(topic, start_time, end_time):

File "/opt/ros/noetic/lib/python3/dist-packages/rqt_bag/bag_timeline.py", line 273, in get_entries for entry, _ in bag._mergesort(bag_entries, key=lambda entry: entry.time):

AttributeError: module 'rosbag.bag' has no attribute '_mergesort'

I'd appreciate it if you could help me out