Support for SermonSpeaker 5.x is in bugfix mode only, the same as it is for Joomla 3.10.
I will not add any new features to this releases.
Please upgrade to SermonSpeaker 6.x and Joomla 4.x, which is better anyway.
Another thing to consider on mobiles: The download rate and cpu power of the devices is much slower than on a desktop computer. So it may take a while till the file is downloaded and will start to play.
Try to make the audio files as small as possible. For example there is no point in storing a speach in stereo, mono is fine and makes it half the size. Also it doesn't need to be 44kHz samlping rate if you're not recording sound. I made good records of a sermon with a sampling rate of 16kHz (about the quality of a telephone). For the bit rate I have it set to 24 or 32kB/s
In US I've seen it as standard everyone uses about 64kbps. I'd do htaccess caching of mp3 files and other files to prevent sending users already downloaded data.
