@early-minister-86776 in case you never worked out why some out of band modifications got reconciled by pulumi and some didn't, it's possible you just happened to change something that isn't monitored by pulumi. There are a few properties which either the AWS api or pulumi don't include yet, could be that you by chance stumbled on one of them. Therefore since Pulumi doesn't know about the particular attribute you changed, it wouldn't change it back.
Another possible explanation could be you mistakenly modified a resource that wasn't a Pulumi managed resource, therefore the change wasn't noticed by Pulumi. I've done this before by deploying to one region, then changing to another region and without noticing and making some changes, then wondering why Pulumi didn't notice