If you haven't already tried this open device care, storage, Advanced. On the page that opens select Other apps, Files, etc for more detailed storage information.
I would try using Files to search for a Folder that contains the highest amount of storage usage. A good one to start with is the Android folder. Long press to select it and a menu will slide up at the bottom of the page. Select Details. This will show how much storage space the Android folder and all its subfolders are using. If it's using 40 or 50 gigabytes then open the folder and select the subfolder titled data. The data folder has a few dozen folders inside so look for a folder related to a gear app or something similar and check the details.
Galaxy S9 SM-G960U
Android 10 One UI 2.0
Security Patch Level
May 1st, 2020
Was this ever resolved?
I am having the same issue and I tried everything imaginable.
Device Care, Emptied Trash, Factory Reset etc. The "other" folder storage is filling up within hours, even though nothing new is being installed.
I've twice found my phone at 60+GB (out of 64), 99% of it in "Other". This could be seen via Settings --> Device Care --> Storage --> Storage Analysis (options menu under top right '...' button). In each case the guilty party was the Samsung Members app (now uninstalled). No updates were reported, pending, or in the process of being downloaded. Prior to uninstalling it the Samsung Members app was up to date as of today (6 Sep 2020).
1. Settings --> Device Care --> Storage will not list "Other", does list "Apps", but does not list "Other" storage consumed by Apps. This page lists user data, and in each case the big consumer was non-user app data, so it only appeared under Settings --> Device Care --> Storage --> '...' --> Storage Settings, where "Other Apps" was the biggest consumer, and selecting "Other Apps" gives you a biggest-first list of apps and their consumption.
2. Settings --> Device Care --> Storage --> Storage Analysis --> Settings is the settings page for the My Files app, not the settings page for storage in general. This is the User Data display of storage consumers and settings, not the one for all data on the device. For the latter you want the list indicated in the above node (1).