As I understand, it was optional to show folder size in SE but enabling it was slowing down folder listing significantly [1.1]. So, instead of computing size of folders, SE adopted a smart approach of looking in Android's file database, MediaStore [1.2]. Some users demanded to see the number of items in a folder next to folder size and this was also implemented [1.3].
[1.1] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/7747836-display-folder-size-by-default
[1.2] https://neatbytes.com/solidexplorer/index.php/solid-explorer-faq/
[1.3] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/6909973-numerical-number-of-folder-items-please-extend

Currently, Solid Explorer can display total count and size of files contained in a folder including all subdirectories unlike other apps. However, accuracy of this information depends on Android’s media scanner. Android’s file database is updated instantly when doing copy & paste operations. However, a file doesn’t seem to be added to Android’s file database in a plausible time after an app creates that file [2.1, 2.2, 2.3]. Some users report that folder size bug is an old one [2.4, 2.5]. The problem seems to compromise FTP [2.3] and FTPS folders [2.6]. SE FAQ recommends waiting but waiting one hour doesn’t help to show that folders are not empty.
[2.1] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/7780158-folder-showing-wrong-file-size
[2.2] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/33550012-directory-sizes-show-as-incorrect
[2.3] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/14815662-list-says-folder-is-empty-but-it-isn-t
[2.4] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/14919357--bug-show-folder-size
[2.5] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/31222429-wrong-folders-size
[2.6] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/11360430-ftps-and-ftpes-shows-empty-folder

Showing folder size is a useful feature of SE. It helps to see which folder is consuming much space and accuracy doesn’t matter much for this purpose. However, since users are inclined to delete empty folders [3.1], accuracy matters when a nonempty folder is about to be shown as empty. Some of my nonempty folders gone forever which are deleted based on this false information. Some users are waiting for recycle bin [no need for reference] and some users want to see size on confirmation dialog [3.5, 3.6, 3.7].
[3.1] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/33546790-delete-all-empty-folders-on-app-start
[3.5] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/8185998-showing-size-when-deleting
[3.6] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/10808730-show-file-size-in-the-delete-file-dialog
[3.7] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/33162865-size-in-confirmation-box

I have some suggestions for empty folder issue. My first suggestion is that SE should continue to get folder size info from Android's file database. That is helpful although is not always accurate. However, total count of files can be replaced with accurate number of first level items. The original proposal of extending folder size info [1.3] didn’t mention to use total count of files but gave examples from an app that count only list first level items. The accurate number of first level items will be more informative than inaccurate number of total number of files. Already, there are many votes to skip amount of files in child folders [4.1]. Reporting the number of first level folders and files separately will also make many users happy [4.2]. So, instead of reporting two inaccurate data i.e. [3141 files | 303 MB], it is better to use at least one accurate data i.e. either [5 items | 303 MB] or [4 folders | 1 file | 303 MB]. This approach is also suitable for situations where folder size can’t be shown. SE choose not to display any count or size information about folders which Android's file database doesn’t provide information (i.e. cloud folders). However, displaying accurate number of first level items is better than displaying nothing.
[4.1] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/11447433-do-not-report-the-amount-of-files-in-child-folders
[4.2] https://neatbytes.uservoice.com/forums/274528-solid-explorer-2-0/suggestions/11447409-differentiate-between-folders-and-files-with-show

My second suggestion is a little experimental but I have to say it. I mentioned that there are some situations where Android's file database is not updated after an app creates a file. That file will not be added to database in a reasonable time because Android runs a full media scan only on reboot and when (re)mounting the sd card. However, it is possible to trigger media scanner even on specific folder [5.1, 5.2]. There is also an app called Media.Re.Scan for this purpose [5.3]. So, seeing a folder as empty even after waiting some time is not impossible to fix inside the app but may be cumbersome and frustrating.
[5.1] https://stackoverflow.com/questions/9414955/trigger-mediascanner-on-specific-path-folder-how-to
[5.2] https://www.grokkingandroid.com/adding-files-to-androids-media-library-using-the-mediascanner/
[5.3] https://play.google.com/store/apps/details?id=com.house.noranuko.mediarescanner