Hey there! I totally get how frustrating those intermittent communication issues can be, especially when they only pop up during certain production runs or environmental conditions. It's like chasing a ghost in the machine! Let me walk you through a systematic approach to tackle this problem.

First, since these issues are timing-specific, start by logging everything: track exactly when failures occur, what machines are running, temperature/humidity levels, and any vibration patterns. This data will reveal patterns you might otherwise miss.

For Mitsubishi servo-PLC communication troubleshooting, here's what I'd check:

1. **Cable and Connection Issues**: Intermittent problems often come from loose connections or damaged cables. Do a 'wiggle test' on all communication cables while monitoring the system. Check for proper shielding and grounding - improper grounding can actually make shielded cables worse!

2. **Environmental Factors**: Since you mentioned specific conditions, monitor temperature and humidity near the equipment. Servo drives and PLCs can be sensitive to temperature fluctuations. Also check for vibration from nearby machinery during those problematic production cycles.

3. **Electrical Noise**: This is a big one! High-power equipment running during specific cycles can create electromagnetic interference. Ensure communication cables are properly routed away from power cables, and check that all shields are grounded at only one end.

4. **Check Mitsubishi Alarm Codes**: Look for specific error codes like AL.36 (SSCNET receive error) or other communication-related alarms in your servo drives. These can give you clues about what's failing.

5. **Power Supply Issues**: Verify that your 24V control circuit power is stable during all conditions. Voltage drops during high-load periods can cause communication failures.

6. **Documentation Review**: Check your maintenance history - has this equipment been moved, modified, or had cables replaced recently? Sometimes the fix is in the paperwork!

The key is to be methodical and patient. Start with the simplest explanations first (loose connections), then work your way to more complex possibilities. Keep detailed notes of what you try and what happens - this pattern recognition is crucial for intermittent issues. Good luck, and let me know if you need more specific guidance!