Hi 
This, actually, is caused by the Telegram Bot API.
Multiple images in one message are always being sent in multiple webhooks from Telegram’s side.
Each with a unique “Message ID”.
This means multiple images sent in one message trigger your scenario multiple times.
In case the images are sent in “Group items” mode, they all have a different “Message ID” but the same “media_group_id”.
I am not really sure whether it could be applied to your scenario idea but you potentially could have one scenario collecting image data with their IDs and “media_group_ids” which you could save to the Data Store and then a secondary scenario that would output (and group) the images data based on the “media_group_id”.
I hope it makes sense.
Cheerio.