Hi @DebsWadge ,
Is the "Wadge" search word existed in the Title column in your SP List?
Does the SearchBox in your app work within your browser? Or same issue as that in your mobile device?
Based on the formula and screenshot that you provided, I could not find any syntax issue with it. If the "Wadge" search word is not existed within the Title column of your SP List, please consider modify your formula as below:
SortByColumns(
Filter('JMS Audit Register', StartsWith(Title, TextSearchBox1.Text)),
"Title", If(SortDescending1, Descending, Ascending),
"SearchColumn", If(SortDescending1, Descending, Ascending)
)
Note: The SearchColumn represents the Text column in your SP list, which used to store the "Wadge" search word.
Also please consider turn off the "Improved app rendering (final validation)" option wtihin Advanced settings of App settings of your app, then re-publish your app, run your app in mobile device again, check if the issue is solved.
Best regards,