One issue that can cause the HMI to freeze or respond very slowly is large graphics in the HMI program. This requires extra processing by the CPU to resize the graphics when the windows change. If you have imported custom graphics into the Picture Library, make sure they are properly sized before importing into the library so that they do not exceed the size of the screen. For example, in the case of the HMI5070L, the screen size is 800x480 pixels so any graphics imported into the Picture Library should not exceed 800x480 pixels.
Oftentimes, erratic behavior by the HMI is caused by something else in the system such as noise or grounding issues. Any kind of transient spike on the power supply or ground could cause the HMI to freeze or stop responding. We recommend that the HMI be powered with a dedicated +24VDC power supply outfitted with AC noise filtering. Make sure the third pin on the power connector to the HMI is connected to a solid earth ground and that the PLC is also connected to the same earth ground. DO NOT connect the “–“ side of the +24VDC supply to earth ground.
Are there any VFDs, contactors, or motors nearby that could be generating RFI or EMI into the communication cable or other electrical wiring? Transient spikes on the power supply or radiated energy from motors, relays, or contactors can get picked up by the cabling and transferred to the HMI. VFDs in particular are notorious for generating high-frequency noise into the environment (conducted and radiated).
We have Technical Note 1027 on Grounding and Noise Issues
that may provide some ideas for isolating the HMI from external noise: