There seems to be an interaction bug between the mask and the filter in Chrome. You can avoid this by doing the mask inside the filter using feComposite and reversing the order of mask and image: pull in the image to the filter using feImage, and use the SourceGraphic to define the mask.
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="400px" height="350px" >
<defs>
<filter id="myfilter" filterUnits="userSpaceOnUse" x="0" y="0" width="400" height="350">
<feGaussianBlur stdDeviation="20" result="reverse-mask"/>
<feImage x="0" y="0" width="400"
height="350" preserveAspectRatio="none" xlink:href="https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Wilsons_Promontory_National_Park_%28AU%29%2C_Big_Drift_--_2019_--_1683.jpg/1280px-Wilsons_Promontory_National_Park_%28AU%29%2C_Big_Drift_--_2019_--_1683.jpg"/>
<feComposite operator="in" in2="reverse-mask"/>
</filter>
</defs>
<g filter="url(#myfilter)">
<ellipse cx="50%" cy="50%" rx="35%" ry="35%" fill="white" />
</g>
</svg>(p.s. it's a good idea to post complete self-contained working code with an image URL that works - e.g. if the CSS classes are not relevant - remove them.)
Wow this really helped thank you so much!