Continually have to reset an App Specific Password for Mozilla Thunderbird. What is going on?

I use Mozilla Thunderbird as my email App for my iCloud email account on a Windows desktop computer. I have been doing this for over a year and a half now.

On 2019-06-07 I was required to set up an App Specific Password for my Thunderbird App.

Everything was working fine. I was able to open up Thunderbird every time without having to re-enter the App Specific password as Thunderbird remembers the password. The only exception to this is if I turned off my computer (I usually leave it running) then I would have to enter the current password and it would work.

Recently I have been not able to open up my iCloud email account in Thunderbird with the current password, and have to generate a new App Specific Password for the Thunderbird App. This has been happening more frequently. (I am not Revoking the password and it still shows in my history)

On 2019-11-19 I had to generate a new App Specific Password for Thunderbird as Apple would not recognize the current password for the Thunderbird App.

Then on 2019-11-21 I had to generate a new App Specific Password as Apple would not recognize the current password. I had to do this twice this date, and I didn't even close the Thunderbird App.

Today 2019-11-22 again the same issue. Overnight I didn't close the Thunderbird App or turn off my computer, and Apple isn't recognizing the current password forcing me again to generate a new App Specific Password for Thunderbird.

As I mentioned this happens whether or not I close the App. After a certain amount of time passes I am having to generate a new App Specific Password for the Thunderbird App.

What is going on? What has changed recently at Apple to cause this frustrating occurrence?

Any help to rectify this situation would be greatly appreciated.

Thanks in advance.