Down connection

Hi!
Sorry for my english.
I have RB951G with RouterOS v5.26.
When I do a backup, I get an error: backup,critical error creating backup file: could not read all configuration fil

Also, about once a day I have lost access to external ports of the router (web, ssh). Rebooting the router does not help. Service is restored after restoring the backup. What could be the problem?
The problem started about a week ago.

It might be radical.
Do a netinstall and try again
Maby is er a disc error