I know this has been reported for older versions but I have the same issue on SQL Server 2017 - when running an SSIS package from the SSIS catalog, using SQL Agent, which calls other packages using Execute Package task, the package will abort suddenly, and the only error shown in the SSIS catalog reports is execution status ends with "Unexpected Termination." There are no "error message" proper. Is this still a problem in the current version of 2017?
Edit with add'l information: I don't know if this is a factor or not but I note that some packages following this pattern do work when they use only database connections in their execution (e.g. getting data from a SQL Server) but the failing packages are reading from Excel workbooks. The failing packages will typically start, locate the file, read it and load it into SQL Server and then, anecdotally at least, the process aborts before the next step after that.