Thunderbird 91.5.0 Scroll bar issue

I'm having trouble in Thunderbird with scrolling through an open email window. Whether I've double clicked an email message to open in a new window or if I have an email up in the 3 way split screen (Folders/Message List/Selected Email Message), once I move off of the opened email I lose the right scroll bar. It doesn't reappear when I hover over the email scroll area or anywhere in the email message. The only way to get it back is by clicking to another email and then clicking back to that previous email or if I manually scrub through the email message and force it to scroll the scroll bar reappears. The scroll bar also doesn't stay up for very long after I've moved off the scroll bar. This also happens in the Preferences and Settings windows, basically any window that has scrolling anywhere in the program. Please advise. Thank you.