"I know it's well known the cannabis use can stop dreaming, or make it very hard to recall dreams. But, now, as I use more cannabis to help sleep and vape and smoke -- my dreams are back and quite vivid. Any reason?"
Most people who smoke marijuana have less dreaming as you have indicated. Most dreaming occurs during the REM phase of sleep and for whatever reason when people use marijuana this time during REM is decreased, which leads to little or no recall of dreams.
But as with most things marijuana, everyone's experience may not be the same. Some people do report having more vivid dreams, and i am not sure of the cause of this. What I can say however, is that many times switching up a strain or a product can alter one's experience, whether that be with sleep or pain, etc.
So, perhaps you may want to consider trying numerous strains and or tinctures or edibles to see if your experience varies. I know many people who consider edibles to be far more effective for a deep slumber.
Lastly, I assume you are smoking an indica before bed and not a sativa, which would energize you and possibly enhance REM sleep time.
I am not a doctor and this post represents my opinion and research only. I hope this helps!