Before yesterday I had killed 3 dragons, Crestwood, Hinterlands and the Exalted Plains dragon without any trouble from Level 13 to 18. Yesterday afternoon I tried to fight the Storm Coast dragon and I seriously was not able to do more than 5% damage before my party was obliterated. Today I tried the Sandy Howler and again it took 15 minutes to do about 20% damage before being smashed.
I am playing as a Rogue Archer (and have previously) and am now L21 and whilst fighting the Sandy Howler, it appeared that some of my shots were not even doing damage at all or they were randomly only doing 10% of the damage they should do.
Probably unrelated but whilst walking around the Hissing Wastes just prior to this fight, first Iron Bull lost 90% of his health for no reason and a minute later the same happened to Cassandra.
I have played the game 3 times already and once over L15 had no problem taking down the lesser dragons and by L18 the tough ones.
All the party have good armor, and weapons such as The Axe of Dragon Slaying, The Axe of Green Edges and I am using a bow that does almost 200 damage.
Anyone else getting any problems like this?
LOL? What?
...But honestly, the dragons are kinda easy and FUN in this game.
Sadly, all you really need is Resist-Tonics and then things are even EASIER and sadly, too face-roll at that point.
You're at the point in the game where Resist-Pots can be purchased from first-level, 2nd second floor in val royeaux store (2 merchants with masks and one of them sells schematics for tier 2 equipment.)
Perhaps if the tonics schematics are not available for sale yet, this could be due to not completing enough side-quests etc in other areas...
BTW, i loved your signature format... had to borrow it

Hint 1: Storm-coast dragon... all electric, get those electric pots or re-build armors and add resist to electric (Again, get your tier 2's from Val Royeaux if you don't already have stuff laying around.)
I don't remember if Sandy Howler is fire or electric... but yea, he's on the harder side because of Armor+ Buff/ AOE stun / and Summoning Mobs... But, again, those resist are so important.
EDIT: OP, I see from later posts that you have decently high resistance...
Question...Hmm, are you mostly using crafted gear or store-bought gear for dps and armors? Sadly, Hissing-Waste (Sandy Howler) at your level out-scales store-bought weapons/gear... All of your stuff really should be Tier 3 crafted Gear at this point.
My main rogue at lv 20 has 432+ dps and 413dps on main-hand and off-hand daggers.
To be fair, i had 300+ dps weapons since lv13 because I found a lucky tier 3 dagger schem and quickly crafted 400+dps daggers with Dragon Bone after slaying Hinterlands dragon/ and Crestwood Dragon.