R error in mutate(across()), Can't subset columns that don't exist

Question

my apologies I am very new to coding.

I have two dataframes (unique*_*pt_all, denom_2011) with the same columns but different number of rows of patients:

> colnames(unique_pt_all)
> [1] "DESY_SORT_KEY"                   "STATE_CODE"                      "COUNTY_CODE"  
> [4] "SEX_CODE"                        "RACE_CODE"                       "AGE"  
> [7] "REFERENCE_YEAR"                  "C_DRY_EYE_COUNT"                 "C_SJOGRENS_COUNT"  
> [10] "C_AA_KERATACONJUNCTIVITIS_COUNT" "C_DIABETES_MELLITUS_COUNT"       "C_POA_GLAUCOMA_COUNT"  
> [13] "C_CICATRIZING_COUNT"             "C_CORNEAL_DISORDER_LENS_COUNT"   "C_CORNEAL_ULCER_COUNT"  
> [16] "C_CATARACT_COUNT"                "C_KERATOPLASTY_COUNT"            "C_PTERYGIUM_COUNT"  
> [19] "C_CORNEAL_ULCER_MIN_DT"          "C_CORNEAL_ULCER_MAX_DT"          "C_CATARACT_MIN_DT"  
> [22] "C_KERATOPLASTY_MIN_DT"           "C_PTERYGIUM_MIN_DT"

I want to add all of the values in columns 8-18 from dataframe "denom_2011" to the existing values in the same columns in dataframe "unique_pt_all" if the value in column "DESY_SORT_KEY" in "denom_2011" match AND the value in column "C_CORNEAL_ULCER_COUNT" is <= 2 in dataframe "unique_pt_all".

I've tried:

columns_to_add <- c(
  "C_DRY_EYE_COUNT",
  "C_SJOGRENS_COUNT",
  "C_AA_KERATACONJUNCTIVITIS_COUNT",
  "C_DIABETES_MELLITUS_COUNT",
  "C_POA_GLAUCOMA_COUNT",
  "C_CICATRIZING_COUNT",
  "C_CORNEAL_DISORDER_LENS_COUNT",
  "C_CORNEAL_ULCER_COUNT",
  "C_CATARACT_COUNT",
  "C_KERATOPLASTY_COUNT",
  "C_PTERYGIUM_COUNT"
)

# Update values based on conditions
unique_pt_all <- unique_pt_all %>%
  left_join(denom_2011 %>% filter(C_CORNEAL_ULCER_COUNT <= 2),
            by = "DESY_SORT_KEY",
            suffix = c("_unique", "_denom")) %>%
  mutate(across(all_of(columns_to_add), 
                ~ifelse(is.na(.x_unique), .x, .x_unique + .x_denom))) %>%
  select(-ends_with("_denom"))

However I'm getting the error:

Error in `mutate()`:
ℹ In argument: `across(...)`.
Caused by error in `all_of()`:
! Can't subset columns that don't exist.
✖ Columns `C_DRY_EYE_COUNT`, `C_SJOGRENS_COUNT`, `C_AA_KERATACONJUNCTIVITIS_COUNT`, `C_DIABETES_MELLITUS_COUNT`, `C_POA_GLAUCOMA_COUNT`, etc. don't exist.

Edit: Including the column names after left join:

colnames(unique_pt_all) [1] "DESY_SORT_KEY" "STATE_CODE_unique"
[3] "COUNTY_CODE_unique" "SEX_CODE_unique"
[5] "RACE_CODE_unique" "AGE_unique"
[7] "REFERENCE_YEAR_unique" "C_DRY_EYE_COUNT_unique"
[9] "C_SJOGRENS_COUNT_unique" "C_AA_KERATACONJUNCTIVITIS_COUNT_unique" [11] "C_DIABETES_MELLITUS_COUNT_unique" "C_POA_GLAUCOMA_COUNT_unique"
[13] "C_CICATRIZING_COUNT_unique" "C_CORNEAL_DISORDER_LENS_COUNT_unique"
[15] "C_CORNEAL_ULCER_COUNT_unique" "C_CATARACT_COUNT_unique"
[17] "C_KERATOPLASTY_COUNT_unique" "C_PTERYGIUM_COUNT_unique"
[19] "C_CORNEAL_ULCER_MIN_DT_unique" "C_CORNEAL_ULCER_MAX_DT_unique"
[21] "C_CATARACT_MIN_DT_unique" "C_KERATOPLASTY_MIN_DT_unique"
[23] "C_PTERYGIUM_MIN_DT_unique" "STATE_CODE_denom"
[25] "COUNTY_CODE_denom" "SEX_CODE_denom"
[27] "RACE_CODE_denom" "AGE_denom"
[29] "REFERENCE_YEAR_denom" "C_DRY_EYE_COUNT_denom"
[31] "C_SJOGRENS_COUNT_denom" "C_AA_KERATACONJUNCTIVITIS_COUNT_denom" [33] "C_DIABETES_MELLITUS_COUNT_denom" "C_POA_GLAUCOMA_COUNT_denom"
[35] "C_CICATRIZING_COUNT_denom" "C_CORNEAL_DISORDER_LENS_COUNT_denom"
[37] "C_CORNEAL_ULCER_COUNT_denom" "C_CATARACT_COUNT_denom"
[39] "C_KERATOPLASTY_COUNT_denom" "C_PTERYGIUM_COUNT_denom"
[41] "C_CORNEAL_ULCER_MIN_DT_denom" "C_CORNEAL_ULCER_MAX_DT_denom"
[43] "C_CATARACT_MIN_DT_denom" "C_KERATOPLASTY_MIN_DT_denom"
[45] "C_PTERYGIUM_MIN_DT_denom"