A solar panel's stated rating is measured under defined test conditions. It is normal for the power you see on an RV to vary throughout the day and to be below that figure much of the time.
Start with the conditions
Cloud, low sun, the direction the vehicle is parked and shading from trees or roof equipment can reduce output. Even a small shaded area can matter, depending on the panel arrangement. Dirt can also affect performance; follow the panel manufacturer's cleaning instructions and avoid climbing onto the roof to investigate.
Check what the system needs
A nearly full battery may not accept as much charging power. Some readings show power entering the battery after other loads have taken their share, rather than the total power available from the panels. Check what your display is measuring.
Compare readings at similar times and in similar conditions before concluding there is a fault. Note the battery state of charge, any running appliances and any displayed warning.
If output has changed sharply in otherwise comparable conditions, contact your installer with those observations and the panel and controller model details. Leave wiring and connector checks to a qualified installer. Prepare a useful support request.