Music stops playing on two devices in a large group after a long time

[Judgeless]

Here is my setup.

5 3rd Gen Echo Dots with no clock
1 3rd Gen Echo Dot with a clock
2 Echo Inputs
2 Echo 5" Shows
1 4th Gen Echo Dot with no clock
11 Total

They are all in a 'Everywhere' group and plays music throughout the house.  And they are working well.  The issue is after about 6 hours two of them stop as if they had a timer on them to stop playing. Same two every time. The are the 4th Gen Echo Dot with no clock and the 3rd Gen Echo Dot with the clock.  The rest keep playing.  Is there a setting somewhere that I can change to stop that?

It is not a network issue.  I can tell one of the devices to stop and then start playing again and those two play with the rest of the group for about 6 hours again