Elemental Theme forced on New Pages despite being inactive

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I am building a new site for a client and, despite Elemental be inactive and Bitter Theme being the active theme, all new pages are created using Elemental theme with no option to choose the active them until it is saved. I then have to go into Sitemap and change it to Bitter. I'm running 8.5.1 with PHP 7.1.

barkingtuna