GSA Per Diem API not returning results for cities with special characters

We recently found that the GSA Per Diem Rates API is no longer returning results for cities with apostrophes. We confirmed that in March, the API accepted requests for cities containing apostrophes in their names. Now the API does not return any results for cities with apostrophes.

Below is an example of an API request that was successful in March, but is now failing to return results:
https://api.gsa.gov/travel/perdiem/v2/rates/city/O%27FALLON/state/IL/year/2023?api_key=REDACTED

It appears that the same behavior is happening in GSA’s per diem look up site as well.

To add context, we noticed the API went down the night of June 8th. Was an update performed in the API that might have created this change?