Check what the ad restriction alert says. Consider the particular words used in the alert for clues that can help reverse the block imposed, for several alerts might appear.
Look if any ad units got relocated or for layout modifications that could have introduced issues.
Check if the app does not have a substantial amount of traffic that is not from individuals who are interested in the app content. If not, switch off or block any possibly harmful sources.
Incorrect traffic gets frequently generated by unintentional clicks. Checking if there is enough space between adverts and other clickable elements on all popular device types will help.
If the traffic originates from sources other than organic search, examine it objectively to see if there is anything about it that would bother advertising.