WordPress fix Child theme Stylesheet missing after updating to WordPress 4.9.4

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Child theme Stylesheet missing after updating to WordPress 4.9.4, by singensmythe

Hi
On Monday Everything was fine with our site but as soon as I updated to version 4.9.4 yesterday (Tuesday) I noticed that there were styles missing from our active child theme. I went into Appearance > Themes and sure enough it said Stylesheet is missing.

However, weirdly enough there are some media queries that I wrote into the stylesheet that still work when the browser is resized and the stylesheet is still there when I checked over the FTP?

Thanks in advance.

Child theme Stylesheet missing after updating to WordPress 4.9.4