In relation to C-5, C-10, CX-20, CX-30:
While digital signage remains available on these models starting from firmware version 2.22, it is no longer officially supported due to critical security enhancements. These updates have significantly impacted performance, often causing signage content to load slowly or fail entirely depending on the platform and media used
In case you still want to use Digital Signage, you can adjust the content to require less memory by using smaller resolution images, less or no animations on the content and avoid the use of video in the signage content.
Alternative, you can choose to remain on the firmware version 2.21 in order to keep the performance at that time (how-to, see KB12975). However, it is viewed as a temporary solution since bug and security fixes will be in all later versions.