There are cases when the Magento sidebar is missing and not showing. Most likely this is because of the "sidebar" or "sidebar.additional" container has been removed from your theme layout.
In order to fix this issue, please follow the steps below:
1. Look for remove="true" in the theme layout XML files. For this you need to check out all these files in our theme in general:
* - means any folders, file names.
2. Remove or comment lines that look like
<referenceContainer name="sidebar" remove="true" />
<referenceContainer name="sidebar.additional" remove="true" />
3. Save changes.
4. Flush Magento cache and check.
If it does not work then please do the same, but instead of theme folder check the extensions folders that are located in app/code or vendor or make sure that your page does not use 1column or empty layout.