Shoppers are voicing their frustration following a change that caused items being listed as the wrong size.
The second-hand shopping app has revised its sizing categories for women's and children's clothes but did not contact all shoppers about the modification.
Countless users and merchants are posting online claiming that product pages now present an altered size classification compared to what was initially listed because of the remapping.
The company said the new system was more in line with other platforms.
It has advised users to review their products and manually change the size where appropriate, resulting in member annoyance.
Earlier, the measurements included one number and one letter, for instance S/8 or M/10.
The new system has an alphabetical indicator and numerical range for example S/UK 8-10.
For certain items, the measurements have been reclassified - like an L measurement was previously a 12 but is now a UK 16-18.
A fashion influencer, who creates plus-size fashion videos, said the change "makes both selling and buying harder".
"Not many brands say XL is a 20-22," which is what Vinted now does.
Stephanie Gallen, based in Glasgow, said garments she listed featuring size 14 markings were showing in the marketplace as measurements 20-22.
"Should someone sized 20-22 purchase these they will likely be quite upset," she stated.
Charlotte Lunn, based in Derby, explained she became annoyed due to the update requiring manual adjustment the sizing for "all her products".
"This situation is especially annoying, because of my ongoing medical condition and selling on Vinted has been paramount following partial earnings loss," she said.
The platform boasts over 100 million users, comprising 18 million UK members.
It has proved a popular alternative to second-hand platforms like eBay and Depop.
This represents another occasion when a surprising modification on the platform has faced criticism: last year, the service retracted a modification to its shipping options following member complaints.
Lena Voss is a tech enthusiast and freelance writer, passionate about demystifying complex innovations.