Office Add-in hangs on context.sync() when using wildcards in search

Question

I'm trying to write an office plugin to find all telephone numbers and highlight them. I used the code template from the official documentation to write the following search with wildcards:

async function checkForText() {
        // Run a batch operation against the Word object model.
        await Word.run(async (context) => {

            // Queue a command to search the document with a wildcard
            // for any string of characters that starts with 'to' and ends with 'n'.
            const searchResults = context.document.body.search('[0-9]@-', { matchWildcards: true });

            // Queue a command to load the font property values.
            searchResults.load('font');

            // Synchronize the document state.
            await context.sync();
            console.log('Found count: ' + searchResults.items.length);

            // Queue a set of commands to change the font for each found item.
            for (let i = 0; i < searchResults.items.length; i++) {
                searchResults.items[i].font.color = 'purple';
                searchResults.items[i].font.highlightColor = 'pink';
                searchResults.items[i].font.bold = true;
            }

            // Synchronize the document state.
            await context.sync();
        })
            .catch(function (error) {
                console.log('Error: ' + JSON.stringify(error));
                if (error instanceof OfficeExtension.Error) {
                    console.log('Debug info: ' + JSON.stringify(error.debugInfo));
                }
            });
    }

The only line that I have modified is the search expression.

If I run this code on a single line of text it seems to work fine, but if I run it anything more the plugin hangs (forever) at the line await context.sync();. Weirdly, using just the wildcard expression '[0-9]@' finds all sequences of numbers in a large document with no issue.