PostgreSQL Error: Connection to the database failed: Server Closed the connection unexpectedly

Question

when I connect to the PostgreSQL Database from localhost then sometimes it gives Error: Server Closed the connection unexpectedly although when execute the command again immediately then connection gets established. but it become a problem because I am using batch files for backups. and sometimes pg_dumpall and pg_dump command also gives Error: Server Closed the connection unexpectedly. and this interrupts my scheduled backups. I have PostgreSQL 12.10 installed on Windows.