Members of the platform have expressed outrage due to a modification that led to items being listed as the wrong size.
The popular resale platform has altered its size classifications for women's and children's garments but did not contact all shoppers about the modification.
Many shoppers and sellers have taken to social media stating that platform listings now display an altered size classification versus the original listing because of the remapping.
The company said the revised method more closely matches similar services.
They have suggested members to review their products and adjust the sizing manually when needed, causing user dissatisfaction.
Before the change, the sizes had both numerical and alphabetical indicators, for instance S/8 or M/10.
The updated approach includes a letter with a size spectrum like S/UK 8-10.
For certain items, the measurements have been reclassified - for example a size L was formerly size 12 but now shows as UK 16-18.
A fashion influencer, who creates plus-size fashion videos, said the change "makes both selling and buying harder".
"Few clothing companies classify XL as 20-22," which is what Vinted now does.
Stephanie Gallen, based in Glasgow, stated items she posted with size 14 tags were showing in the marketplace as larger sizing 20-22.
"If anyone [who is] size 20-22 buys them they may become frustrated," she explained.
A different user, based in Derby, stated she felt frustrated by the change as she had to manually change the sizes on "every single listing".
"For me this is particularly frustrating, since I have chronic health issues and platform income has been essential for me since losing part of my income," she said.
The app has more than 100 million users, including 18 million in the UK.
It has emerged as a preferred choice compared to resale services such as eBay and Depop.
This is not the initial instance where an unanticipated change to the app has proved unpopular: last year, the platform withdrew an update regarding delivery choices due to shopper criticism.
Lena Visser is techjournalist met focus op startups en digitale transformatie in Eindhoven.