If you’re using a post loop template and the post excerpt is not showing, there are a few things you can try to troubleshoot the issue:

Check the settings of your post loop template to make sure that the «Excerpt» field is selected and set to be displayed.
Check your theme’s template files to ensure that the_excerpt() function is being used to display the excerpt in the loop.
If you have a custom function for displaying the excerpt, check that it’s being called correctly in the template.
Deactivate any 3rd party plugin that may be conflicting with the excerpt display.
Check if your theme have some setting for excerpt and it’s enabled.
If none of the above steps work, you can try using the manual excerpt field in the post editor to manually add an excerpt for each post.
If you have further question please let me know.