Possible cause for some loops might be the SD
I lately got some reboot loops on my I9505 (4.2.2 still).
The first few times I wiped it all and started from scratch but it was getting annoying.
I noticed some users stating that removing the SD will fix it and it did, although it does not help if most of your stuff is on the SD card.
The next thing I wanted to investigate is what on or with the SD might have caused the troubles.
a) no damaged sectors or problems found with Windows tools
b) all data could be copied on the HDD
c) SD could be formatted and all previously sved things copied back on the SD
Still once the SD was in and the phone started it was stuck again, but at least a faulty SD was ruled out.
And here comes my first mistake:
I checked the SD and all looked fine, so I wasted a few hours on useless tests.
Much much later I finally found the culprit: one of the ASEC files had been corrupted!
The are stored in a hidden folder ".android_secure" on the SD.
Once the phone get's stuck in this loop the SD will suffer some sort of damage to the data structure caused by the faulty ASEC file.
I turned the phone on without the SD,
formatted the SD again (with the tool from SDCARD.org) and put all data back on,
mounted the SD and checked the menu.
One program was greyed out and claimed it was not installed.
Unmount again, deleted the corresponding ASEC file and restarted the phone - success!
No more loop and after WiFi was eneabled the missing app received an update and was woking again too.
I do realise this problem is not always the cause of the dreaded reboots and loops we might get, but checking for corrupted files with the instructions above might save you a lot of time investigating.
Another thing I noticed is that for some reason the stuff from the SD loads much faster (on the phone) if the SD was formatted in the phone and not in the card reader on the PC.
As possible cuses for thes file corruption I can point to apps crashing and modifications to programs with Lucky patcher or similar while parts of the program are still active in the background - even if it is just the notification part.
I hope this info might help some people here to get their phone working again or maybe even to find a fix for the problem altogether.