I'm using Tomcat 8.5.9. It appears that query strings containing percent encoded ampersand (%26) and percent (%25) characters are not parsed correctly when using the HTTP/2 connector. Using HTTP 1.1, it works fine.

To reproduce:

1) create ROOT/test.jsp with these contents:

foo=[<%= request.getParameter("foo") %>]


2) Set up an HTTPS connector in server.xml that upgrades to HTTP/2 and start the server:
<Connector port="8443" scheme="https" secure="true" SSLEnabled="true" compression="on" address="0.0.0.0">
        <UpgradeProtocol className="org.apache.coyote.http2.Http2Protocol" />
        <SSLHostConfig protocols="TLSv1.1+TLSv1.2">
            <Certificate certificateKeyFile="conf\tls\key.pem"
                         certificateFile="conf\cert.crt"
                         certificateChainFile="conf\tls\STAR_credentialsmart_net.ca-bundle" />
        </SSLHostConfig>
</Connector>


3) Browse to https://localhost:8443/test.jsp?foo=b%26a

The result is:
foo=[b]

4) Now comment out <UpgradeProtocol ...> in the HTTPS connector in server.xml and restart.

5) Browse to https://localhost:8443/test.jsp?foo=b%26a

The result is:
foo=[b&a]

The access log also shows the URLs differently:
0:0:0:0:0:0:0:1 - - [15/Dec/2016:02:12:22 -0500] "GET /test.jsp?foo=b%26a HTTP/1.1" 200 14
0:0:0:0:0:0:0:1 - - [15/Dec/2016:02:12:36 -0500] "GET /test.jsp?foo=b&a HTTP/2.0" 200 12

And the logs show the message:
14-Dec-2016 23:48:59.846 FINE [catalina-exec-2] org.apache.tomcat.util.http.Parameters.processParameters Parameter starting at position [10] and ending at position [15] with a value of [10] was not followed by an = character