Ok. First thing first, I have experienced this bug on both of my saves ( both on survival difficulty). I post this bug report on both steam, and bethesda.net and I didn't get any solution. It seems there are quite few people that actually experienced same or similar bug. The GUN is my last hope since I am already 78 hours in game and I don't want to start all over again. The bug is stated blow:
"So I have encountered few people who have same bug. On survival mode, I noticed my strength get's set to 1 with a ( - ) sign next to it while I don't have any active (de)buffs. My strength in perk tree menu is 9 but when switch to pip-boy character menu is strength 1 ( - ) without any active effects. For now, I have tried enter and exit power armor, using console commends (player.setAV and player.modAV) on both survival and very hard and none of these works. I saw people mentioned if you sleep with many (de)buffs it is most likely you will encounter this bug and currently I can't find any solution with it. I am already 78 hours in game and my last save which doesn't contain this bug is only 4 hours in game. Any one got similar bug or solution please response."
To add on this, it is not caused by party boy/party girl perks nor mole rat diseases since I don't have either of them. It doesn't necessary have to be strength, can be other stat. Anyone who has experienced same bug please report.