60%

Yeah, I started one day last week like this at work. From 8am until about 1:30pm I kept encountering the JB stalling at 20, 30 and 60%.

My combination finally was iTunes 12.1.0.71 (open at the time I ran the JB), Airplane mode, running as Admin. However, this was on a Windows 7 PC (32 bit) with a 32 bit install of iTunes. Even so, I had to run it twice before it jailbroke.

Hope something here helps.

 

Or try another restore and give it a shot again JB.

 

Try finding a windows computer to JB it with.

 

You should also try another iPhone cable, and try re-jailbreaking it several times, it might continue further each time.

 

This is what FINALLY worked for me... I was too stuck on 60% for days. Several restores and re-jailbreak attempts, always 60%. Reboots never seemed to work. This is what finally worked:

1. Sync phone and make a backup.
2. In itunes "Restore iPhone" with new iOS 8.4 Do NOT restore from backup once reformatted, but instead setup as new phone.
3. Jailbreak phone
4. Now go back into iTunes and "Restore Backup" from your previous backup in step 1. That will restore your settings, apps, etc but still keep the jailbreak.

I was going nuts with the 60% until I tried this.