Haven't seen a 'disappearing' issue in 17.36. When starting a brand new project, go to OPTIONS | DISK tab and Clear Unused Cache Files.
It's unclear exactly what you are attempting with Zoom and Stretch, but the order that effects are applied can make a difference.
In this example ZOOM isolated the red circle. Then the Stretch to Aspect Ratio effect was added. Choose the aspect ratio from the drop-down menu.
If that's not what you were doing, please explain more fully. Capture and link a video if possible. Upload the file/s to a free server, such as Google Drive or MS OneDrive, right-click the link and Share or Copy. Copy the result and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, click SHARE | SHARE and change "restricted" to "anyone with link can view.**
Zoom_Stretch.mp4