I would suggest to start with checking browser language settings and machine region settings. The display of date format changes with regional\language settings of user machine & browser. The browser settings can get updated with regular windows patches.
Example (Using different language settings):
English (United States)[en-US] - 2019-01-09 13:44 EDT (YYYY-MM-DD...)
English (United Kingdom)[en-GB] - 09/01/2019 13:49 EDT (DD-MM-YY ...)
It is possible that these date formats were changed as result of customization. However,I would rule out this for now.
Hope this helps.!