Discord UseLocalAvatar option does not work for most users

[lewisakura]

Describe the bug
The UseLocalAvatar option does not apply avatars to most users even when they have associated Discord accounts. We are using Matterbridge in a 30k member Discord server, and upon review of the source code it seems like Matterbridge is only caching a subset of our users (which even then sometimes does not work until ages later).

To Reproduce
Unsure if it's easy to reproduce, see above context.

Expected behavior
Matterbridge would request users as needed instead of relying purely on cache.

Screenshots/debug logs

Environment (please complete the following information):

• OS: Oracle Linux Server 8.8 aarch64
• Self compiled: 56e7bd0

Additional context
matterbridge.toml

[irc]
    [irc.libera]
    Server="irc.libera.chat:6697"

    UseTLS=true
    SkipTLSVerify=false
    UseSASL=true

    Nick="[redacted]"
    RealName="[redacted]"
    NickServNick="[redacted]"
    NickServPassword="[redacted]"

    ColorNicks=true

    RemoteNickFormat="<{NOPINGNICK}> "

[discord]
    [discord.[redacted]]
    Token="[redacted]"
    Server="[redacted]"

    AllowMention=["users"]
    ShowEmbeds=true

    AutoWebhooks=true
    UseLocalAvatar=["irc.libera"]
    ShowJoinPart=true

    StripNick=true

    RemoteNickFormat="{TENGO}"

    UseUserName=true
    EditSuffix=" (edited)"

[tengo]
RemoteNickFormat="/etc/matterbridge/remotenickformat.tengo"

[[gateway]]
name="[redacted]"
enable=true

    [[gateway.inout]]
    account="irc.libera"
    channel="#[redacted]"

    [[gateway.inout]]
    account="discord.[redacted]"
    channel="[redacted]"

/etc/matterbridge/remotenickformat.tengo

text := import("text")
result = text.to_lower(nick)