double single pole switch not working

Replaced a stacked single pole switch. One switch (top) operates an outside patio light and the other (bottom) operates 4 ceiling mounted l.e.d fixtures. At first it worked fine but now, a week later, it's acting screwy. Top switch does not turn on patio light and bottom switch only turns on 3 out of the four l.e.d lights. It gets worse, when top switch is on the "on" position and you turn bottom switch to "on" the fourth ceiling mounted l.e.d light, which was prieviously off, turns "on" and the other 3 become dim.

1) Is switch bad? I am assuming that the 2 switches (top and bottom) should be completely independant of each other and in this case they seem to interact with each other.

2) Assuming switch is bad, why do only 3 out of 4 ceiling l.e.d lights work under one scenario and only one (and the others dim) under the other scenario?

Any help out there would be most appreciated. Thank You.