I do not know, but, the last round fired could have been too hot, the last person to fire the rifle could have experienced resistance to bolt opening and put the rifle away. There is spring back/recovery, my cases after being hammered have short memories measured in milliseconds so it is not likely a fire case recovered over a long period of time, enough to cause resistance to bolt opening.
Clean the chamber, examine the case for corrosion, oxidation or electrolysis due to dissimilar metals?
And examine the case head for signs of high pressure, flatten primer, case head expansion? and marring of the case head caused by the bolt, this happens when the case is locked to the chamber when the bolt is rotated.
F. Guffey