Thunderbird portable keeps deleting accounts

Hi!
My Dad's Portable thunderbird keeps deleting accounts. It happend second time today. Maybe it's because the device lost power when using Thunderbird. At the first time, which was a few months ago, I didn't find any good solution for this -> I created accounts again, and packed old emails into local folder. But now I started to think if there is any solution to get rid of crashes like that? For me it wouldn't be a problem but it's my dad's flash drive with his work correspondence... Can I restore the old accounts or I really need to create them again and move mail files manually? I started to think this is not a good app solution for him... Cheers!

EDIT: when I tried to see verision of TB it shows 68.12.0 and started an update.
EDIT2: Ok so I've created a new clean account and thunderbird automaticaly download "new" e-mails (pop3). They start in may this year and end today. But I have another inbox folder where are another emails received in last months (including may-september), and another one (third) inbox folder where are emails up to 2019. I wan't every of this three inbox folders to merge into one. Is it possible or do I need to create different local folders in Thunderbird like "old", "new", "newest"?