Shipped .jar files are created by me.

You can recreate them like this:

.viaproxy/plugins/ViaProxyOpenAuthMod.jar

This is completely unchanged https://github.com/ViaVersionAddons/ViaProxyOpenAuthMod/releases/download/v1.0.2/ViaProxyOpenAuthMod-1.0.2.jar. Check for yourself:

sha256sum .viaproxy/plugins/ViaProxyOpenAuthMod.jar
# 95085aac381ae92fc45d476732958b826254be4fbe2876f2d8b619b2373898fe  .viaproxy/plugins/ViaProxyOpenAuthMod.jar
curl -L https://github.com/ViaVersionAddons/ViaProxyOpenAuthMod/releases/download/v1.0.2/ViaProxyOpenAuthMod-1.0.2.jar | sha256sum
# 95085aac381ae92fc45d476732958b826254be4fbe2876f2d8b619b2373898fe  -

.viaproxy/ViaProxy.jar

1. go into viaproxy
2. src/main/java/net/raphimc/viaproxy/proxy/util/ExceptionUtil.java
3. modify ExceptionUtil.handleNettyException

4.  public static void handleNettyException(ChannelHandlerContext ctx, Throwable cause, ProxyConnection proxyConnection, boolean client2Proxy) {
        if (!ctx.channel().isOpen()) return;
        if (cause instanceof ClosedChannelException) return;
        if (cause instanceof CloseAndReturn) {
            ctx.channel().close();
            return;
        }
        if (!client2Proxy || !ViaProxy.getConfig().shouldSuppressClientProtocolErrors()) {
            Logger.LOGGER.error("Caught unhandled netty exception", cause);
            // @SOPHER CHANGE START
            //try {
            //    if (proxyConnection != null) {
            //        proxyConnection.kickClient("§cAn unhandled error occurred in your connection and it has been closed.\n§aError details for report:§f" + ExceptionUtil.prettyPrint(cause));
            //    }
            //} catch (Throwable ignored) {
            //}
        }
        // literally never close
        //ctx.channel().close();
        // @SOPHER CHANGE END
    }