Unable to compile class for JSP after migrating from EAP 6 to 7

Issue

We are upgrading our application from EAP 6.0 to EAP 7.3.1. While trying to connect to one of our application features, we are seeing the following exception:

    javax.servlet.ServletException: javax.servlet.ServletException: org.apache.jasper.JasperException: JBWEB004001: Unable to compile class for JSP.
    (...)
    Caused by: java.lang.NumberFormatException: For input string: "${i+j}"
            at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
            at java.lang.Integer.parseInt(Integer.java:569)
            at java.lang.Integer.valueOf(Integer.java:766)
            at org.apache.jasper.compiler.JspUtil.coerceToInt(JspUtil.java:571)