Yeah, that's a problem. Assuming that the amount does not represent the amount of earnings distributed, a code 8 2019 Form 1099-R indicates that the elective deferral that was returned was an elective deferral made for 2019, not your excess elective deferral for 2018.
It appears that you'll be forced to file a substitute Form 1099-R (Form 4852) to dispute the code 8 reported on the Form 1099-R, to explain that the payer refuses to correct the coding and to explain that this elective deferral was included on your 2018 tax return and that there were no investment gains attributable to this excess contribution that needed to be distributed. On the page where you select the type of Form 1099-R you are entering, TurboTax has a box to indicate that you need to file a substitute Form 1099-R (Form 4852). Doing so will require mailing your tax return.
https://www.irs.gov/taxtopics/tc154
