M5300-52g slow start up when using v11 firmware

During a deployment of a stack to replace an existing one, I ran into a problem.

Instead of lift and shift of both units, the 52 port switch running v11 firmware (pre configured) was plugged into a live older switch (running v10). This then sent both switches into a tailspin and broke the configuration of both old and new hardware.

The old stack has been restored, however I still need to replace with the 5300 stack. The new M5300 52g switch is showing some VERY strange behaviour even after factory reset and multiple firmware updates and factory resets.

Initially after the incident, I had to force a reset using the CLI and to perform a hardware reset from there. Incidentally, all the ports apart from the USB, on the switch just weren't working or detecting any cables. Once I eventually got into the GUI, I could see that it was showing both elements of the v10 AND v11 firmware together.

Having followed advice from within this forum, I have loaded v.10.0.0.53 to the switch. This then boots up fine and the ports on the front become live within 90 seconds. However, if I upgrade the same switch to v11.0.0.40 and reboot, It then takes 7 minutes before I can ping it and get access to the GUI. I'm simply not willing to rebuild and deploy this switch until I get this behaving as it was prior to the incident.

Please note. I'm pinging the default private addressing 169.254.100.100 and I'm not worried about the config as it's going to need a fresh build.

Old kit

GSM7228PS and a GSM7352Sv2. Running v10.0.0.53

New kit
M5300 52g and M5300-28g-PoE+. Desired firmware V11.0.0.40

I feel I have exhausted all my options and would welcome any other suggestions.

Thanks in advance.