(My friend in real life gave me this)That's the original sequence:

⬅↕➡,⬅↕,➡,⬅,?,?,↕➡

I'm going to use other symbols to make it readable:

(/), (/,), (/, ?, ?, /)

I've noticed that the comma initally moves to the left,in fact we have a full symbol ⬅↕➡ that gets cut by the comma and becomes ⬅↕, and then the other part, goes after the comma ➡ then we start repeating the symbol ⬅↕➡ again,but this time it's still cut because the comma hasn't moved so we just write ⬅, by following the same logic after this there should be ↕➡,and then we have to understand if the comma changes the direction of the movement,because if it moves leftt we get something like this:

⬅↕➡ ,⬅↕,➡,⬅,↕➡,⬅↕➡⬅,↕➡ and I think this one is wrong

but if it switches direction and moves to right we get this: ⬅↕➡ ,⬅↕,➡,⬅,↕➡,⬅↕,↕➡

I think both my solutions are wrong because we should probably get a sequence made only of symbols of 3 and not like those :⬅↕,↕➡ or ⬅↕➡⬅,↕➡. Please help me,than you for your time.

• Is the comma a separator beween each item of the sequence (with each item consisting of one or more symbols), or is each item a single symbol, of which the comma is one? Apr 22, 2019 at 14:35
• @WeatherVane Comma should be seen as a separator beetween each item,with item i mean this:⬅↕➡ in this case that's the first part of the sequence,then we have the repetition of the same item that is sliced by the comma ,basically the comma moves to the left and full symbol ⬅↕➡ becomes ⬅↕,➡ with a comma and the same happens again ,this time the symbol is ⬅↕,➡ that already has a comma ; the comma moves to the left again and makes it become ⬅, I hope I Was clear
– user57534
Apr 22, 2019 at 15:02
• Thanks, I was confused by your remarks about the comma moving around, but they aren't any part of the sequence. Apr 22, 2019 at 15:03
• @WeatherVane Sorry if my explanation was confusing xD
– user57534
Apr 22, 2019 at 15:04
• OK, I reopened it. Though I have the distinct impression that I've seen this exact same puzzle somewhere before... Apr 22, 2019 at 18:16

⬅↕➡,⬅↕,➡,⬅,↕➡,⬅,↕➡

Reasoning:

Without the commas, a continuous pattern is established with less than three characters filling the fields in question... ⬅↕➡⬅↕➡⬅↕➡⬅↕➡

Maybe:

If we convert it into numbers:
123,12,3,1,?,?, 23

Ordered groups of elements of the first member of the sequence that are missing:
2
31
231
312

And the only ones that complete the sequence maintaining the 1-2-3 format are:
2/31

That is

⬅↕➡,⬅↕,➡,⬅,↕,➡⬅,↕➡