Baically your AC compressor is not tripping which results in ice formation over the evaporator due to which airflow decreases.
Go to any Ac guy & ask him to replace/check the thermostat sensor bcz AC is not tripping as it should.
For the time being. when you feel that air flow is decreasing, just switch off the AC not the fan & within 2 to 3 minutes, you will again feel the normal airflow.
Also you can check by noticing the compressor under the hood if it is tripping or not i.e. getting on & off after a specific time.
Baqi nothing to worry about, its minor issue.