No matter how sophisticated an aircraft pressurization system is, if you descend too late and to quickly the cabin can only descend quickly, therefore causing ear disconfort. It is simple maths, elapsed time since begining of descend till landing.
If you add a cough or congestion, you can have your ears damaged.
Many crew members have had problems because of that.
In an airline, many cabin atendants will use the flu as an excuse for not working on a given day (sunday morning, tipically) and many others will have ear problems because they do not want to earn less money or have problems with the company.