I tried to reproduce your problem, without success. My steps:
Setting up in AWS: Ubuntu 18.04 with defaults
Installing v1.6.0p10 CEE
omd create test
Installing v1.6.0p14 CEE
omd update test
omd backup test test.tgz
Copy test.tgz to second AWS instance (with installation of first v1.6.0p10 CEE, then v1.6.0p14 CEE)
omd restore test.tgz -> successful
On the restore target host, what does ‘omd versions’ say as root?