Why do I have hard visible lumps after filler in forehead lines?

Because of the anatomy of the forehead, this area is not very forgiving when a filler is injected.  If after two weeks you are unhappy with the results, the filler can be broken down with hyaluronidase.   

The lumps that you notice could possibly be from swelling, water retention or too much Juvederm. It is best for you to wait 2 full weeks to let the product settle and for the swelling to subside.  If you are still unhappy with the results or notice lumps i would recommend that you book a follow up with your injector to assess.

The onky filler I am using for forehead lines currently (in the United States)  is Beletero, diluted one-to-one and placed just above the lining over the bone. Other fillers are known to cause lumpiness. This may just be swelling, in which case it should get much better in the next few days to two weeks. Try massaging it into place snd use cold compresses. See your doctor for hyaluronic acid injections if this does not improve.

There is swelling after any fillers and Juvederm pulls water to itself right after injection. Your bumps could be from either of these, or it could be too much product in the area. Keep your hands away from the area and don't press on the bumps. If things don't look like you expected about 10-14 days from your initial injection, then see your injector for a follow-up. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."