When selecting the post and print a GL Journal Entry the G/L Register report is run at the end of the post routine.  It is ran with whatever selections have been previously stored in the report the last time it was run.
To set the report to print dimensions you must:

Go to the G/L Register report in the menu and select the report.

Ensure there are no filters on the first 2 tabs.  Go to the options tab and ensure to select the include dimensions option and simply close or cancel the report to save the settings.

If the G/L Register report is ran manually with a filter for a specific register or G/L Entry filter, and these filters are stored in the report the print and post will not print the report.

To correct select the G/L Register report, clear the filter close the report and this should correct the issue.