A new first for me 
The two portals were superimposed… and there was no way to keep going down. Clicking on the portal brought me back up one level. 
I tried hovering the mouse in different spots, especially around the outside of the portal… but no luck. Had to abandon that Vision and exit game (to reset Visions and get another portal).
Perhaps Blizzard can consider having some sort of minimum distance between the two portals…
Had something quite similar some days ago, not to say the same; in the fake Tristram part. My solution was to zoom in and then tried the same as you - and it worked.
And yes to the minimum distance. They fixed the bug with chests appearing in unreachable positions in the visions, so they should be able to apply a fix for that issue too, especially since visions are now part of the normal game and not only seasons.
I’ve wondered if that could happen. It seems to be rare but possible.
What I want fixed is the accidentally entering a vision problem. This is a real pain in the backside for HC especially while leveling. You go to click on an item dropped on the ground, say an interesting legendary, and just as you do another monster dies nearby, spawns a vision, and “Poof!” you’re inside with 3 bosses hovering around the exit. And since the order for hit testing seems to be “monsters first” you can’t click on the exit to get back out. Lost a toon that way in EU this season.
The vision entrance should NEVER appear right next to the player where they’re likely to be clicking to interact with other parts of the environment. Hmm, thinking about it that might fix the overlap problem you saw as well.
I had a few close calls… this one, for example, on 19-Feb-24:
But I was always able to find a way to keep going… just a matter of hovering the mouse over the portals, checking what name pops up and clicking when the right one shows up.
I’ve had that too…
Despite the occasional problems visions have been a blast. My understanding is they’re a permanent part of D3 seasonal play, right?
That’s also my understanding… Time will tell, I suppose.
What? You got these to spawn in non-season?
They don’t? 
Well, have not played non season in quite a while, but I thought they are available there too. If not, sorry for my misunderstanding… 
There are a few threads on this topic particularly.
Yeah, that’s what many of us were expecting along with the Altar when this patch dropped. But alas, the altar appeared in NS on the Asian server for like 2min before disappearing as per post number 4 in this petition thread:
Feel free to drop a like in the opening post and comment in support of getting both features added to NS. Seems rather silly they gated so many massive QoL improvements behind seasons only. The game is in maintenance mode… there really isn’t anything in the nerfed Altar and Fissures that will break the game to the point where it’s broken or unplayable.
I think they have to do fixed points of spawn exits to next lvl as and entrances do. Same for chests.
I could be mistaken, but there’s a specific monster that spawns the Portal (blue) to the next Level. The blue Portal spawns where you kill it.
You can confirm this on Levels that have the Rift Guardians. There are 3 Guardians and 1 monster. The monster spawns the blue Portal to the next Level. If it’s a Treasure Goblin, it’s the last Level and spawns a Diabolical Chest.
If possible, fall back, away from the entrance Portal (red). Let the monsters come to you and kill them when they’re not close to the red Portal. (I know… sometimes easier said than done).
If it happens again, try repositioning your Character. You should be able to position your Character where the Portals are offset enough to click the edge of the appropriate Portal.
(I’ve given up on Blizzard ever fixing these types of anomalies. Just last night I was running a Greater Rift on a “Pandemonium” map. I activated my Potion and had a red Triune Circle spawn off the catwalk, floating in air. 
)
Tried that… didn’t work… believe me, I really tried to keep going down. At that time, I was down 6 or 7 levels/floors, and I really, really wanted that Chest and all its mats.
Yeah… in my defense, I will only say that this was the first time it occurred… so I learned. (I’m old… but I can still learn )
Cheers !