Whatever you want to call the market that Appian plays in - BPM, Case Management, Rapid App Dev - there are some serious challenges to consistent growth. These types of products have been around for a couple of decades now, and are constantly squeezed by pure-play "application" software companies (salesforce, sap, oracle, etc) as well as the unique customization requirements that only custom programming can accomplish. It is not easy selling these products.
Appian itself is one of the least sales-friendly companies I experienced in my 20 years in the space. I felt like a contractor more than an employee, with little investment on their part in developing a collegial sales team either through training or a president's club. I also witnessed sales personnel being terminated for sharing competitive information with their colleagues - I had never seen that before!