This is a common issue caused by Google’s spam detection. Google will remove reviews that violate its guidelines or look like spam. A large number of reviews on Google, but none elsewhere online or reviews that appear in two places are indications of spam. If your reviews are not coming from unique IP addresses, they will be deleted. Reviews left from too far away will be deleted. If there is anything suspicious about the review(s), they will be deleted. Other possible culprits are glitches, bugs, and human error. Regardless of the reason, you cannot get deleted reviews back, so focus on obtaining new, non-suspicious reviews and save new review details from email notifications so you can determine the cause of deletion in the future.