Charitable contribution carryovers retain their % limits for the year the contribution was made. So your 2017 (+ prior yr if any) cash contributions were limited to 50% and any carryover retains that 50% of AGI character.
See Example 1 under Carryovers (p18):
https://taxmap.irs.gov/taxmap/pubs/p526-005.htm#en_us_publink1000229824
