Some m4a files will not load

I am using Audacity 2.0.5 on Win 10 with FFmpeg library installed. m4a files from Voice Memos recorded on an iPhone load OK, but the same format file from an Android Voice recorder shows an empty track. The “Importing FFmpeg-compatible files” box does not appear. The MediaInfo results for each file are below;
Android m4a Media Info.png
iPhone m4a Media Info.png

Actually “empty”, or a flat blue line (silence)?

Just updated Audacity to V 2.3.1 and problem file loads OK!