It is extremely unlikely to be an issue of early hardware. As the previous response indicated it is almost certainly an issue with the feature set of the code running on the router (note this is not a question of version but of feature set). If you look at the output of show version (or even better if you post the output of show version to this thread) you will probably see that the router is running the IP BASE feature set. I believe that you need an upgrade to a feature set with more capabilities to do the encapsulation command.
Your post seems to indicate that you have one router that does support the encapsulation command and one router that does not. I believe that is you compare the two routers you will find that they are running different feature sets.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...