That could have been terrain type. In Archive, if you’re trying it at the part where Mellka is dumping the cookbooks and poetry into the data … minion … thingies, then it could be because of the ground slope - that area is in a depression with sloped ground all around it. I’m quite certain that uneven terrain is problematic. I don’t know why, exactly - it could be that the riptide effect isn’t being applied to ground / terrain on a higher or lower plain, it could be that the graphic and effect diverge on changing terrain heights … I don’t know - but I do know that I, too, couldn’t get it to work on that type of terrain.
If you don’t get credit after a few casts on a specific terrain type, move around. Try to find a terrain that does work. You want something as flat as possible, on ground level, without obstruction or interference by different objects like grass or boxes. Also, don’t forget to walk forward after casting the spell so that your character gets counted.
One thing you can try - if you take the Helix option that heals those standing in the Riptide, you and any other character standing in the riptide should see a little green heart in the bottom left of your screen while you’re under the effect. Take a poll of your team - is everyone seeing the green heart?
Even when I found a spot that does work, I was getting credit for 1/3 or 1/4 of the casts, on average, performed under the exact same circumstances. For me, this was worse in PvE than in PvP. If I were to break it down, I’d say that 1/2 to 1/3 of PvP casts worked, while 1/4 to 1/8 of PvE casts worked.
Don’t give up! It can be done. But don’t bang your head against the wall for long periods when it’s not working - if you don’t get credit after 3, 4, 5 casts or so, try different terrains, missions, characters, and so on. If you find a specific terrain that just doesn’t work, period, post here and I will add it to my list. I know that, for instance, the elevator in Heliophage and the final Isic Magnus boss chamber just don’t work - period, and because of that, I’m almost positive that there are others. Good luck!