Hair stylist

Okay so this sounds weird . I have really thick long hair but recently I’ve been noticing I’ll be brushing my hair and in the back of my hair I have strandes of hair that are clumped together and hard af and crunchy like I got something in my hair but I know that’s not it because it’s happened multiple times after I just got done washing my hair and it dried . I barley use heat on my hair and I haven’t done anything differently . What could it be? Once I brush it and separate the hairs it doesn’t feel like that anymore . Could I just be producing more oil in my hair then usual and it happens to sit and make it hard and crunchy help!!!!