Shoppers are voicing their frustration following a change that caused listings displaying inaccurate size information.
The popular resale platform has revised its size classifications for women's and children's garments without notifying all shoppers about the modification.
Countless users and merchants are posting online stating that platform listings now display a modified sizing category compared to what was initially listed due to the recalibration.
The company said the revised method more closely matches similar services.
The platform has recommended to review their products and manually change the size when needed, resulting in member annoyance.
Before the change, the measurements included a single numeric size and a letter, for instance S/8 or M/10.
The updated approach includes a letter with a size spectrum such as S/UK 8-10.
For certain items, the measurements have been reclassified - for example a size L was formerly size 12 but is now a UK 16-18.
Frankie Bridger, who produces content about larger sizing, said the change "makes both selling and buying harder".
"Rarely do manufacturers list XL as sizes 20-22," as the platform currently indicates.
Another user, from Glasgow, explained products she uploaded with size 14 tags were showing in the marketplace as larger sizing 20-22.
"Should someone sized 20-22 purchase these they will likely be quite upset," she said.
Another shopper, from Derby, explained she became annoyed due to the update requiring manual adjustment the measurements for "each individual item".
"For me this is particularly frustrating, as I'm chronically ill and platform income has been essential after experiencing income reduction," she said.
The app has more than 100 million users, comprising 18 million UK members.
It has proved a popular alternative to second-hand platforms like eBay and Depop.
This is not the initial instance that an unexpected update to the app has proved unpopular: earlier, Vinted reversed a change regarding delivery choices following member complaints.