I have the same problem and I am at a loss for troubleshooting at this point. I have in the past managed to get it to work but now it does not matter how many times I restart php-fpm or reboot the server. unraid-dvb just hangs at updating and exec.php times out just like your error message.
UPDATE: I removed unraid-dvb, updated stock unraid to 6.7.0-rc8 then reinstalled unraid-dvb and it still took awhile but it finally made it past and allowed me to install the new version of unraid-dvb.