Gmail autocomplete -- how to clear contact suggestions when composing a new message?

When I compose a new message in Gmail on my Android phone I'm offered several suggestions for the recipient (i.e. for the email's To: field) via an autocomplete function. These are often very old/unknown contacts which I'd like to no longer see as autocomplete suggestions, but I can't yet work out how to clear this list. The contacts suggested appear to have come from an old list of "Other" contacts, i.e. people that I've contacted infrequently and who were not actual contacts I've added to my contact list. These only show up when I compose a new message in Gmail on my phone, and the autocomplete works as expected when on a non-Android device (laptop). My assumption is that the Gmail autocomplete function is reading these outdated contacts from a list stored somewhere in a file on my phone which is impervious to the contact sync process or somehow not being cleared as expected otherwise -- I've tried all manner of syncing phone contacts, deleting old/other contacts outside of Android, etc. but no joy so far. An idea I have is to somehow search Android's filesystem for a file that contains the unwanted contacts and if found then wipe that file clean. Is this reasonable, and if so can anyone suggest guidance that'll make this less of a wild goose chase? My phone details: Model: Nexus 5X Android version: 7.1.2 Baseband version: M8994F-2.6.37.2.21 Kernel version: 3.10.73-ge570678 Build version: N2G47F Thanks in advance for any help or insight.