Rising EGT while Cruising

I am using Rotax 912 ULS engine on my aircraft. I was recently flying when I got the perplexing beeping alarm of high EGT, when I observed the EGTs values I found EGT4 was rising beyond limit. So I made an emergency landing and checked the EGT probes, carbs, any sources of air leaks from the manifold clamps etc. I tried few tricks few clicks to investigate the cause, so I swappped the EGT3 and EGT4 probes on the engine. Started the engine on ground and observed the values but again I found EGT4 rising gradually till the time it starts alarming. Then I asked my crew to dismantle the carbs and we had a detailed inspection of them, nothing was found. Then I installed the new EGT 3 and 4 probes, started the engine and found the same problem. I checked the probes' values independently on Rotax Flydat as well but the same problem of rising value of EGT4 appears on Flydat too.

Given that I have checked the following things:

CHT and Oil temps are okay and fine.

Spark plug condition is good and normal.

Fuel flow rate is good. I hae also shifted the needle notch a point higher to make the mixture a bit richer to cool down the EGT but the problem remains there.

Now I am amazed why EGT4 only is showing this trend despite of having changed the probe. Why does egt2 not show this rising trend when it is on same side of the engine. What factors do affect this behaviour of rising EGT?