General sense of loss - I would say my DS fits this, he doesn't have any significant issues, like my girls do but he does have insecurities that other kids his age don't have. For him - he tends to be clingy and fears seperation, he tends not to deliberatly disobey rules as he's worried about being rejected. Very unlike my other two, who do/did have very significant issues.
I would say as general adoptive parenting advice - steer away from discipline that implies a form of rejection or being sent away e.g. being sent to the naughty step. Sometimes it works, but I've seen it fail many more times than I've seen it work. With DS when he gets extremely hyper and unregulated, he has 'time in' with me where we both sit quietly together, or he sticks close to me while I do some mundane chores which won't excite him. I have to reassure him a lot that I love him, will always be there etc. Younger children often can't put their big feelings into words, which is when you can get anger, tantrums etc. I know DS has had problems at home and school when he feels upset and doesn't understand why or can't express it, he just stops interacting very much and withdraws.
On the surface he's very similar to other chiildren his age - you could look at his behaviour and wouldn't immediately know that something was 'different'. The difference is that he acts this way for a different reason than other children might withdraw or be clingy, and his fear of seperation is very very real because it's really happened to him.
Loss can be amplified at cetain times, and not be significant at others. IME kids seem to become much more aware of their beginnings at around 7-9, and I've seen quite a few adoptees of this age go through periods of feeling very sad about it all. I don't think that's preventable, it's just them developing their understanding of their story which includes the realisation that they have lost out in their life. It will probably pass, but you can't hurry that, just generally be nurturing and patient, and be able to explain their story to them carefully. If you've never had any issues before, it can be a more challenging time for parents
'Challenging times' - well, my challenging times have been very bad. Luckily DD1 is a generally very happy adult now with a few issues, but we have had some very horrible times. Not a general loss thing though, very specific to her past