We have evaluated your presented scenario on our end while using the latest version of Aspose.Cells for Java 8.3.0.4, and we are able to replicate the said problem. The process seems to hang while extracting the chart from your provided spreadsheet in image format. We have logged the problem in our bug tracking system under the ticket CELLSJAVA-41119 for further investigation & correction purposes. Please spare us little time to properly analyze the problem cause, and to provide the fix at earliest possible. In the meanwhile, we will keep you posted with updates in this regard.
I am afraid, the ticket attached to this thread is still unresolved. We have recorded a note for the concerned development team member to share the insight of the problem, and most preferably an estimated release schedule for the fix. As soon as we receive any updates in this regard, we will post here for your kind reference.