This worked for my Galaxy s4. I panicked when the password limit got down to four. I turned off the phone, removed and reinserted the battery, and turned the phone back on. The old password worked on first try after this reboot. Pretty simple and the least complex solution to try before other more difficult solutions.
I was having this exact problem today with my phone. I initially tried to restart it; it didn't work. Then I tried turning it off and on and, again, it didn't work. I found this thread though and went to findmymobile.samsung.com on my laptop. I was able to change the pin and lock my already locked phone from there. Once the hour I had to wait was up, I was able to unlock my phone using the pin that I had set through find my moblie. I mostly relieved that I was able to fix the issue this way without having to factory reset. I really wanted to avoid that.
I had the same problem but it was the lock pattern that wasen't working. When it didn't work after I completely shut it off and turned it on again (a few times), I turned it off and waited the alloted time to reset (1 hour) then turned it on and the lock pattern worked.
I'm experiencing the same issue. had the phone less then a week. I switched from an s6 on verizon to a s7 on ATT. Battery ran down yesterday and phone powered off then wouldn't accept pin on powerup. did factory reset last night. ran through setup, all was fine. It was late so I didn't go through restoring backups. This morning, I have same issue. I just tried the google android device manager. It says since device has a lock set, it won't accept it even though I can see the message I input on the screen.
Prior to this happening yesterday, I had to uninstall and reinstall Uber, and received an Uber update. Was able to use the app just fine and was using the app when the battery drained.
Wiped cache before and since factory reset and again after using Androind device manager. Samsung Find my mobile didn't work either even tho device was registered before factory reset.
Have used a S6 for over a year and the same password for much longer. Setup this phone with the same password and used it to unlock it a few times after powerups, until last night. Any suggestions?