On the Twitter support site, Twitter says that for iOS users who had more than one account on Twitter and opted into sharing location information on one account, location data may have been collected when using any other account on the same device, even if location features were not activated.
Twitter also says that some of that location data was mistakenly sent to one of its advertising partners, but the data was "fuzzed" so that only zipcode or city data was shared. The location data was not able to map precise movements nor was it tied to Twitter handle.
Separately, we had intended to remove location data from the fields sent to a trusted partner during an advertising process known as real-time bidding. This removal of location did not happen as planned. However, we had implemented technical measures to "fuzz" the data shared so that it was no more precise than zip code or city (5km squared).Twitter says that its partner did not retain the location data and it was only available on their systems for a short time before it was deleted.
This location data could not be used to determine an address or to map your precise movements. The partner did not receive data such as your Twitter handle or other unique account IDs that could have compromised your identity on Twitter. This means that for people using Twitter for iOS who we inadvertently collected location information from, we may also have shared that information with a trusted advertising partner.
Due to a bug in Twitter for iOS, we inadvertently collected and shared location data (at the zip code or city level). We have fixed the bug, but we wanted to make sure we shared more of the context around this with you. More here: https://t.co/n04LNt62Sa— Twitter Support (@TwitterSupport) May 13, 2019
The bug that caused the inadvertent data collection has been fixed and Twitter says it is "working hard to make sure it does not happen again." People with accounts who were impacted with this issue are being notified.