Error when running the module below

[akassirach]

from sklearn.model_selection import StratifiedShuffleSplit

sss = StratifiedShuffleSplit(n_splits=2, test_size=0.5, random_state=42)
train_indx, test_indx = next(sss.split(unique_ids, unique_labels))

train_ids = [unique_ids[ind] for ind in train_indx]
train_labels = [unique_labels[ind] for ind in train_indx]
print(len(train_ids), len(train_labels))

test_ids = [unique_ids[ind] for ind in test_indx]
test_labels = [unique_labels[ind] for ind in test_indx]
print(len(test_ids), len(test_labels))

ValueError: The least populated class in y has only 1 member, which is too few. The minimum number of groups for any class cannot be less than 2.