I started to wonder how is it possible to remove finished (or even ongoing) process instances using SQL from activiti tables? Just removing from act_hi_taskinst table doesn't work, giving some errors while starting server.
Yes, of course I've tried to undeploy process from console, that was the first thing I thought about, but it hadn't resolved the ""Error loading items" share issue, so that's why I made for tampering with database manually.