High CPU usage from Node when some serial devices are not switched on

[SailorMacSailface]

Hello, 
i recently noticed that the raspberry pi was working with high load, "Node" process is showing 300% CPU load on "top".
Three external devices connected via serial, depth sounder, ais and vhf where not switched on. 
Once these were switched back on the cpu usage dropped to around 4% again. 
In the signalk server log I found lots of entries reading: 

Code:

bind EADDRINUSE 169.254.133.250:2053 at node:dgram:359:20 at processTicksAndRejections (node:internal/process/task_queues:84:21) { errno: -98, code: 'EADDRINUSE', syscall: 'bind', address: '169.254.133.250', port: 2053 }

How can I prevent that from happening? 
I do want to be able to switch various instruments off while still using openplotter. 

Anyone have a clue? 

Thanks a lot