Yanmar, and some other motors, in some installations have wire runs with voltage drops through the engine control panel to the starter solenoid.

The solenoid needs to "see" enough voltage to actuate it. If your battery (or bank) that's starting the engine is down a bit, nothing may happen when you turn the key or press the starter button. The simple cure is to put a small relay that will cause the battery to connect directly to the solenoid. The relay is less sensitive to lower voltages.

The second issue is sometimes a shifter 'cutout' on some engine "shifters". On some systems, the linkage needs to be in "nuetral" in order to protect against starting the engine in reverse or forward. if the shifter is out of alignment or the cut-out is not wired correctly, or whatever -- nothing will happen when you try to start it. The problem may be "infrequent'.

We had the first condition of the voltage being below the solenoid trigger level. The simple relay fix kept me from having to run below and show my unwholesome upbrinng by jumping the engine. (Doing that in a hurry can be somewhat shocking or, in the worst case, you weld the screwdriver to some piece of grounded metal and have a very bad situation.)

Of course, I thought it was our Vetus shifter, but alas, it was not a Dutch treat.