Try adding "loadSync=true" to your posters.
Unfortunately, loadSync="true" does not fix the issue.
I changed the code to display all digits so that it is easier to stop/start the screensaver and see if there is an issue. And whether I use loadSync="true" or not, the issue always pop up after a few tries (less than 20)...
The code could not be simpler:
<component name="Digits" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" extends="Group" xsi:noNamespaceSchemaLocation="http://rokudev.roku.com/rokudev/schema/RokuSceneGraph.xsd">
<children>
<Poster id="d0" translation="[0, 0]" uri="pkg:/images/clock_0.png" width="66" height="92" loadSync="true"/>
<Poster id="d1" translation="[56, 0]" uri="pkg:/images/clock_1.png" width="66" height="92" loadSync="true"/>
<Poster id="d2" translation="[112, 0]" uri="pkg:/images/clock_2.png" width="66" height="92" loadSync="true"/>
<Poster id="d3" translation="[168, 0]" uri="pkg:/images/clock_3.png" width="66" height="92" loadSync="true"/>
<Poster id="d4" translation="[224, 0]" uri="pkg:/images/clock_4.png" width="66" height="92" loadSync="true"/>
<Poster id="d5" translation="[280, 0]" uri="pkg:/images/clock_5.png" width="66" height="92" loadSync="true"/>
<Poster id="d6" translation="[336, 0]" uri="pkg:/images/clock_6.png" width="66" height="92" loadSync="true"/>
<Poster id="d7" translation="[392, 0]" uri="pkg:/images/clock_7.png" width="66" height="92" loadSync="true"/>
<Poster id="d8" translation="[448, 0]" uri="pkg:/images/clock_8.png" width="66" height="92" loadSync="true"/>
<Poster id="d9" translation="[504, 0]" uri="pkg:/images/clock_9.png" width="66" height="92" loadSync="true"/>
<Poster id="d:" translation="[560, 0]" uri="pkg:/images/clock_separator.png" width="66" height="92" loadSync="true"/>
</children>
</component>
