DC Power Issue

I ran through all the voltage checks again:
Shore power off (no power to trailer)
Solar panels not covered/full sun.
Solar controller panel reads error (can’t detect a battery)
Across battery: 12.8V
Battery - to fuse + : 12.8V
Battery - to CB near battery: both sides 12.8V
Cover solar panels
Solar controller panel goes blank
Across battery: 12.75V
Battery - to fuse + : 12.75V
Battery - to CB near battery: both sides 12.75V
Plug in shore power (solar panels still covered)
Solar controller panel indicates 13.7V (no indication that battery is being charged)
Across battery: 12.77V
Battery - to fuse + : 12.77V
Solar panels not covered/full sun.
Solar controller reads charging up to “13.8V / Full”
Unplug shore power
Across battery: 13.58V
Battery - to fuse + : 13.58V
Cover Solar panels
Across battery: 12.9V
Battery - to fuse +: 12.9V
Controller panel shows 12.7V
Turn on lights sequentially until all lights fail.
Turn off all light switches. Switch on lights (none light).
Return all light switches to off position.
Across battery 12.8V
Battery - to fuse + : 12.8V
Next steps/any ideas?