FWIW, I originally wrote the program with an UNO board but then trimmed it down for use on an ATTiny44 at 8MHz
Is the problem also seen on the UNO as well as the ATTiny44? Sounds like it may be a memory issue (which is often the case in scenarios where x number of y types works, but when I add one more, it doesn't work, and it doesn't matter which one is added). The ATTiny44 has far less SRAM/EEPROM/Flash memory than the UNO.