How to see all tagged resources in Cost Explorer

I created User-defined cost allocation tag "customer" on a few years ago.

I have tagged most of our resources in AWS over 5 months ago. I have been the only one doing the tagging.

I noticed that two our i3.2xlarge instances can only be listed under filter "No tag key: customer" even though I have given the resources the tag with Key: customer and Value: value3. Cost value was around $650

When I filter with tag customer:value3, it shows our g5.xlarge with same tag value and also tagged S3 and EC2-Other resources. I verified that this is the case also by using Dimension: Instance type. It lists the i3.2xlarge in there with cost value $0.00.

Also, AWS Resource Groups, Tagging, Tag Editor will find the i3.2xlarge instance with the customer:value3, so the tag definitely exists. Seems weird that some of tagged resources are showing as tagged and some are not.

Edit: I tried to find differences in tagging using aws ec2 describe-instances -output but could not find any. The commands which I ran are listed below:

user@ubuntu-server:~$ aws ec2 describe-instances --instance-id i-xxxx --region eu-north-1 > aws.describe.i3.2xlarge.json
user@ubuntu-server:~$ aws ec2 describe-instances --instance-id i-yyyy --region eu-north-1 > aws.describe.g5.xlarge.json
user@ubuntu-server:~$ grep -e "Tag" aws.describe.i3.2xlarge.json
                    "Tags": [
user@ubuntu-server:~$ grep -e "Tag" aws.describe.g5.xlarge.json
                    "Tags": [
user@ubuntu-server:~$ jq .Reservations[].Instances[].Tags aws.describe.i3.2xlarge.json
[
  {
    "Value": "i3.2xlarge server",
    "Key": "Name"
  },
  {
    "Value": "value3",
    "Key": "customer"
  },
  {
    "Value": "Production",
    "Key": "stage"
  }
]
user@ubuntu-server:~$ jq .Reservations[].Instances[].Tags aws.describe.g5.xlarge.json
[
  {
    "Value": "value2",
    "Key": "customer"
  },
  {
    "Value": "Production",
    "Key": "stage"
  },
  {
    "Value": "g5.xlarge server",
    "Key": "Name"
  }
]