Hello, JSTGH1. Thank you for posting this question to the Apple Support Communities.
We understand your situation and how you are noticing that your saved text replacements seem to be removed automatically from your iPhone. We know that you must depend on this feature and we’re happy to help you find out what could be causing this.
To get started, we would like to provide you with the following Apple Support article. This article explains how you can save keystrokes and text replacements on your iPhone. Please be sure that you are using these instructions as you add new text replacements to your device:
Save keystrokes with text replacements on iPhone - Apple Support
At the bottom of the article, you will find instructions for reseting the iOS Keyboard Dictionary. We may suggest this before you start to add your text replacements again. Please note that this step would remove all custom words and shortcuts that you have enabled now. This also returns the keyboard dictionary to the default state.
Please reply back here if you have any questions about these steps.
Have a great day!