If you have TreeShare set to automatic login and the Ancestry API is off line it will cause the index to flash. The other time if does that is if the password is bad. You can reset it by using the key command Ctrl+Shift+U in a main view. Select "Reset Program Settings" restart RM and it will be cleared.
Keep in mind it might just be the connection with Ancestry itself.
Message from Ancestry (4 Jun 2018)
"We wanted to reach out to our customers and reinforce our commitment to you and the safeguarding of your important work on family discoveries. We highly value every customer and regret that a small portion of our customers are experiencing issues as we complete our migration to a more powerful computing environment that will enable us to serve you better. We are committed to providing more content, more connections, enhanced hints, and streamlined search to make your discovery process even more enjoyable. Please know that your data is safe and secure at all times. For example, if you have any data loading issues, please be reassured that all of your work on your trees remains intact and will return. Our dedicated technical teams are working 24/7 to ensure that any remaining issues are resolved as quickly as possible. If you have any questions or concerns, please do not hesitate reach out to our customer service specialists."