Creative fatigue happens when the same people see the same ad too often and stop reacting to it. Your ad did not get worse. Your audience got used to it.
Three signs
- Frequency climbs past about 3.5 in a week for a prospecting audience.
- CTR drops while spend stays the same.
- Cost per result rises slowly over several days.
What to try
Add a new creative in the same ad set rather than editing the old one, so you do not reset learning. Change the first three seconds, not only the colours. Widen the audience a little if the audience is small. Wait two days of data before you judge the new ad.
What not to do
Do not double the budget to "fix" it. A tired creative with more money just gets tired faster.
Rules of thumb are guides, not laws. Check your own numbers.