SYMPTOM
In Strategy Web, the side toolbar disappears for a specific user after minimizing the Side Toolbar and subsequently navigating through folders:

CAUSE
It's a known issue in Strategy Web that occurs when cookies are disabled on the Strategy Web Administrator Page > Security > Cookies Security level:

ACTION
This issue will be addressed in Strategy 10.4 Secure Enterprise Platform Hotfix 4 and Strategy 10.8 Secure Enterprise
WORKAROUND
Set "Cookies Security level" to "Enable cookies" option from the Strategy Web Administrator Page > Security > Cookies Security level.
Note: The suggested workaround makes reference only to the "Enable cookies" option. Do not enable the "Store Strategy Intelligence Server sessions information in temporary cookies instead of on the Web server" option.
KB423975