A distribution from a Roth 401(k) is not permitted to be rolled over to a traditional IRA. Doing so results in a potentially partially taxable distribution to you of the cash from the Roth 401(k) due to the deposit into the traditional IRA being a failed rollover. The cash deposit into the traditional IRA is then a separate, independent regular traditional IRA contribution.
The only fix is to notify the traditional IRA custodian that this deposit constituted a regular contribution, not a rollover to the traditional IRA, obtain a return of contribution from the traditional IRA before the due date of your tax return (with the amount distributed being adjusted for attributable investment gain or loss, then completing a late, indirect rollover to a Roth IRA under IRS Rev. Proc. 2020-46 of the original distribution amount (regardless of the adjusted amount distributed from the traditional IRA).
If you instead leave the funds in the traditional IRA, any amount over the amount that you would be eligible to contribute as a regular traditional IRA contribution for the year would be an excess contribution subject to a 6% penalty each year that the excess remains in your traditional IRAs.
Any amount rolled over to the traditional IRA from the traditional account in the 401(k) can remain in the traditional IRA as a successful rollover.
