not able to select correct email address to do the encryption

[XXLUncleM]

Hi Professions.

I have encounter this problem when sending an encrypted email.
I had exchanged keys with account A and his key is with my keyring. His ID is valid.

When I try to send email to him, you know, by selecting his name in the mailvelope pop up window, it is not auto selected.
And when i type the full email address, it shows me that key not found.
I really took a look on his key and found the only potential issue, which his key has 2 unknown signee, but really long long before.
I could sent him an encrypted email in 2022, not sure what happened after that.
If anyone knows what should I do now?