What has probably happened over time is dirt and water and whatever has worked its way down into the seam and finally working each side up.
I do hate to tell you, but this is a tell tale event to let you know that its about time for a new floor.
But, as a band aid, you can gently pull up or with a putty knife lift up an inch or so one each side of the line. Then carefully clean up all the junk from the area. Do not too much water, as you want this perfectly dry when you go to the gluing step.
After all the junk is out, apply some special projects liquid nails under the side flaps and wait about 10 minutes, then push the areas down and wipe away all the residue that spurted up.
Now, you want to apply some weight to both sides to hold the curled edges down and seal. Remember, if you have any glue showing, the weights will be glued down also. I would put wax paper over the crack area and then put weights on that.
It might take a while for the curl to settle back down, you might have to use a hair dryer as a persuader.
Now, after about 24 hours of drying, take the weights off and it should be fixed. Now, you need to get some clear 100% silicon and fill into the crack to make sure nothing especially water gets back there. Use clear.
Let this dry for another 5 hours or so.
If this does not work, you did not clean out the junk well enough.