Reproduced today with EO-Browser (a lot of 500 in console):
apps.sentinel-hub.com
Sentinel-hub EO-Browser3
Sentinel-2 L2A imagery taken on August 18, 2018
And with a sample WFS request for DSS2:
https://services.sentinel-hub.com/ogc/wfs/ACCID?SERVICE=wfs&WARNINGS=True&REQUEST=GetFeature&TYPENAMES=DSS2&BBOX=53.1498598892%2C38.9996937994%2C54.1481041035%2C40.6803358683&OUTPUTFORMAT=application%2Fjson&SRSNAME=EPSG%3A4326&TIME=2020-05-07T00%3A00%3A00%2F2020-05-29T23%3A59%3A59&MAXCC=100.0&MAXFEATURES=100&FEATURE_OFFSET=0
Response is a strange-looking 500:
<?xml version='1.0' encoding="UTF-8"?>
<ServiceExceptionReport>
<ServiceException>
<![CDATA[ Invalid response code from the index service: 500 ]]>
</ServiceException>
</ServiceExceptionReport>