Thank you for your post.
If the find worked previously but no longer works, something has changed. With the find issue happening more frequently, I suspect there is some damage to the file. However, let's first uninstall and reinstall FileMaker Pro, just in case the FileMaker Pro application is damaged. See if this works.
Assuming the issue continues with a new installation, check to see if this is a field issue. To check this, create a new field, and replace the contents of the new field with the value from the original field. Perform your finds on this new field. If this works, then you can delete the old field and rename the new field to the old field name.
If the problem still exists, then export the data to a text file, and then open a backup file from a month ago. Delete the records and import from the text file so you have the most up-to-date information. Now try Finding. Does this work?
Keep me updated with any progress.
Thank you for the quick reply. Will test and give you an update.