Regarding PDI issue

[Gajendra singh]

Developer Instance is undergoing unscheduled maintenance. Get Notified when your PDI is available.

[anurampalli]

This will take 8 to 12 hours to resolve. Sometimes, it resolves faster too. Just wait. If it doesn't get online, unfortunately, you have to release instance and request a new instance. If you are keen on having the same release, then, also, unfortunately, you won't get an older release instance. 

[svirkar420]

Hi @Gajendra singh , Though its not clear what you want to say, but if PDI is going into unscheduled maintenance or in a sudden maintenance then this is not an issue you need to worry about, this has happened a lot with me. 
Just try to refresh the PDI from "https://developer.servicenow.com/dev.do" page 1-2 times and then wait for some time and then log in again, this will help you retrieve your PDI.

If this solution helped you Please Mark this solution as accepted and helpful as it will be helpful for other users as well.
Best Regards.
Saurabh V.

[Nikhil Bajaj9]

Hi @Gajendra singh ,

If PDI is going in maintenance, no one can tell you when it will be back. Once Maintenance is completed, you will get an email that maintenance completed. Check your PDI at this time. Unfortunately there is no support available on PDI.

[Ravi Gaurav · Accepted solution]

After 2021.. ServiceNow stop taking backup and stop supporting any issues in PDI.
Maintenance is temporary please wait for 24-48 hours it will be back ..
If there is no data you can request a new one