Same here. Happened a few days ago and had to reset. Again today about 21:00 GMT+1.
Spain, stock FP3, latest updates installed, Operator DIGI Spain.
Looks like a software issue IMO, Im gonna try to downgrade to an older version to see what is going on.
Vodafone again?
did anyone try to run the phone without SIM?
Yes, doesn’t help at all after the problem started to appear. Also reboots to factory reset 20 seconds after unlocking the screen without SIM.
My very wild guess was: Since it worked for me for six days after the last factory reset, maybe they are sending “something” over the air only sometimes and that triggers the problem starting.
Who is they?
However good its not another Vodafone Germany issue as it also happens in Spain😉
Tried all possible combinations: With/Without SIM/SD card/flight mode/safe mode 
Did another factory reset. Problem reappeared this time within 10 min after factory reset…
Next idea: Unlock bootloader, downgrade to previous firmware version. I know that one has issues with bluetooth, but if it at least let me use my phone again…
Never done that. Is there a good How-To including links to where to download older versions?
The network providers? Don’t know exactly what they really can or cannot push over the air, but since I learned that they can hold back OS updates, I thought maybe they can also push settings that result in this.
done the downgrade to previous version…didnt even last 10 minutes before the factory reset started.
Thing is, my wife which also has the same FP3 (bought both at the same time), same update, same SIM card company, has no issues at all 
Installing lineageOS for now, cant have no phone due to work. This sucks
Hi and welcome to the fourm:
Note Yvmuells post above
DIGI Spain uses Vodafone
This issue just started appearing for me as well now. I have only a TelekomDE sim in my fp3, in the SIM2 slot, so it’s definitely not a vdfn issue.
I wasn’t even actively using the phone at the time it happened, so it’s fairly likely that it’s some OTA stuff.
This happened me last Friday aswell. Reset within phone didnt help. Tried several times. Same issue.
What i did. Unlocked bootloader, performed offline install on pc twice and relocked bootloader.
Formatted sdcard on pc before booting up phone
It has worked now for 6 days
It started happening for me too just a few minutes ago…
I hope there will be a fix soon, I kind of need the Phone
Original FP3, had it for about 2.5 years. Telecom Germany, so not exclusively Vodafone
Can I somehow unlock the bootloader without going through the settings?
Otherwise, I only have the 20 second window until it reboots. That’s kind of stressfull.
I experience exact the same problem since this morning. I have tried again, tried to go back to factory settings etc, but it keeps happening…
Probably don’t worth to try: My phone was stuck in the bootloop again minutes after downgrading and entering my PIN.
It happened to me an hour ago. I am stuck at the screen clabalde and JohnLBevan posted. It rebooted by itself in the middle of the night and this morning, while writing a short message, it suddenly rebooted with ending in this continuous loop.
Hi, had the same thing on Nov 4. after 10 reboots did the factory reset and reinstalled everything. It worked till this mornong. Now back in the black screen. Does Fairphone know about the issue?
I always get the error massage “LocationServices has stopped” and then after about 10 seconds it reboots and shows the black screen as in Post#1
I have oppened a ticket with fairphone support with a link to this thread. please do the same https://support.fairphone.com/hc/en-us/articles/115001041206
Not when you dont tell them, so everyone please #contactsupport and def refer to this topic. As support is slow, call them once you have your ticket number and make this really urgent
Related Reddit thread: https://www.reddit.com/r/fairphone/comments/yrqjqc/need_help_with_a_weird_bootloop/
I also opened a ticket with the fairphone support with a link to this thread - so far no response.