This code removes all old user roles if a new user role is assigned when subscription status is changed.

um_woocommerce_subscription_status_changed_remove_old_roles.php

<?php 

// Remove all old roles on subscription status change.
function um_woocommerce_subscription_status_changed_remove_old_roles( $subscription_id, $old_status, $new_status ) {
	global $wpdb;

	if ( ! UM()->WooCommerce_API()->api()->is_wc_subscription_plugin_active() ) {
		return;
	}

	$subscription = wcs_get_subscription( $subscription_id );
	$userdata     = $subscription->get_user();

	if ( empty( $userdata ) || is_wp_error( $userdata ) || UM()->WooCommerce_API()->api()->maybe_skip_user_by_role( $userdata->ID ) ) {
		return;
	}

	$arr = array(
		'active'         => '_um_woo_product_activated_role',
		'pending'        => '_um_woo_product_downgrade_pending_role',
		'on-hold'        => '_um_woo_product_downgrade_onhold_role',
		'expired'        => '_um_woo_product_downgrade_expired_role',
		'cancelled'      => '_um_woo_product_downgrade_cancelled_role',
		'pending-cancel' => '_um_woo_product_downgrade_pendingcancel_role',
	);

	$items = $subscription->get_items();
	foreach ( $items as $item ) {
		if ( empty( $arr[$new_status] ) ) {
			continue;
		}

		$new_single_role_query = $wpdb->prepare(
			"SELECT meta_value
			FROM {$wpdb->usermeta}
			WHERE user_id = %d
			  AND meta_key = %s", 
			$userdata->ID,
			'_um_woo_subscription_' . $subscription_id . '_product_' . $item->get_product_id() . '_' . $new_status . '_role'
		);

		$new_single_role = $wpdb->get_var( $new_single_role_query );

		if ( empty( $new_single_role ) || 'ignore' === $new_single_role ) {
			continue;
		}

		if ( ! in_array( $new_single_role, $userdata->roles, true ) ) {
			$userdata->add_role( $new_single_role );
		}

		foreach ( $userdata->roles as $role ) {
			if ( $new_single_role !== $role ) {
				$userdata->remove_role( $role );
			}
		}
	}

	UM()->user()->remove_cache( $userdata->ID );
}
add_action( 'woocommerce_subscription_status_changed', 'um_woocommerce_subscription_status_changed_remove_old_roles', 20, 3 );

This code is a patch that changes the roles assignment logic for subscriptions in the extension Ultimate Member - WooCommerce. This code removes all old user roles if a new user role is assigned when subscription status is changed.

Add this code to the file functions.php in the active theme directory to use.