IIS Request Filtering Issue

Question

I'm setting request filtering rule on IIS:

<security>
    <requestFiltering>
        <filteringRules>
            <remove name="test" />
            <filteringRule name="test" scanUrl="true" scanQueryString="true">
                <scanHeaders>
                    <clear />
                </scanHeaders>
                <appliesTo>
                    <clear />
                    <add fileExtension=".aspx" />
                </appliesTo>
                <denyStrings>
                    <clear />
                    <add string="Demo" />
                </denyStrings>
            </filteringRule>
        </filteringRules>
    </requestFiltering>
</security>

And when I'm testing URL: https://localhost/Demo/app.aspx rule is working, but only for first 2 times, IIS log:

2021-04-27 21:08:30 127.0.0.1 GET /Demo/app.aspx - 443 - 127.0.0.1 Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64;+rv:88.0)+Gecko/20100101+Firefox/88.0 - 404 19 0 78

2021-04-27 21:08:49 127.0.0.1 GET /Demo/app.aspx - 443 - 127.0.0.1 Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64;+rv:88.0)+Gecko/20100101+Firefox/88.0 - 404 19 0 0

2021-04-27 21:08:49 127.0.0.1 GET /Demo/app.aspx - 443 - 127.0.0.1 Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64;+rv:88.0)+Gecko/20100101+Firefox/88.0 - 200 0 0 31

After app pool restart filtering is again working only for first 2 requests. Did someone had similar issue? Or any suggestions?