KafkaConsumer fails to "Re-Subscribe"

My Task is to write some Python3-Scripts to test an apache-kafka system. Therefore, from every topic-partition pair, one message should be read. The routine subscribes to a topic and goes to a random offset in a topic-partition, reads a message and unsubscribes. E.g. that means, that it subscribes, unsubscribes and then "re-subscribes" to one SAMPLE_TOPIC, to check partition 0 and 1. The "re-subscribe" step seems to fail but I have also encountered it, that the first subscription step fails, which I fixed using the partitions_for_topic-Function.

I know I could implement it without un- and "re-subscribing", but if possible, I want it to work as stated.

So, what is there going wrong?
Am I missing something? Or Is this due to the design of apache-kafka / kafka-python? Or is it a bug in one of them? Or something else?
I appreciate any help.
Kafka-Python=2.0.2
Apache-Kafka=2.7.0 (According to kafka-topics --version)
Python3.8.5

The code below is a reduced variant of an original which runs in a gitlab-pipeline:

from random import randint
from kafka.consumer.fetcher import ConsumerRecord
from kafka.structs import TopicPartition
from kafka import KafkaConsumer

def output_check(kafka: KafkaConsumer, topic_partitions: list, offsets: list):    
    tp: TopicPartition
    offset_dict: dict
    for tp, offset_dict in zip(topic_partitions, offsets):
        print("\nOUTPUT_CHECK TOPIC_PARTITION:", tp)
        offset: int = randint(offset_dict["start"], offset_dict["end"])
        msg: ConsumerRecord = read_single_message(kafka, tp, offset)
        print()
        print(msg)

def read_single_message(kafka: KafkaConsumer, topic_partition: TopicPartition, offset: int):
    print("BEFORE SUBSCRIPTION - TOPIC:", topic_partition.topic)
    kafka.subscribe([(topic_partition.topic])
    print("\nAFTER SUBSCRIBE - SUBSCRIPTION:", kafka.subscription())
    print("AFTER SUBSCRIBE - ASSIGNMENT:", kafka.assignment())
    print("AFTER SUBSCRIBE - PARTITIONS FOR TOPIC", kafka.partitions_for_topic(topic_partition.topic))

    assert topic_partition.topic in kafka.subscription(), \
        "The Consumer is not subscribed to the given Topic" + str(topic_partition.topic) + "."
    if <OFFSET CHECK>:
        raise ArithmeticError("Offset {} is not existing in {}".format(offset, topic_partition))
    else:
        print("\nAFTER OFFSET CHECK - SUBSCRIPTION:", kafka.subscription())
        print("AFTER OFFSET CHECK - ASSIGNMENT:", kafka.assignment())
        kafka.seek(topic_partition, offset)

    kafka.poll(max_records=1)  # Poll Messages. Might be unnecessary...
    msg = None
    for msg in kafka:
        break
    kafka.unsubscribe()
    return msg

The Topic-Name and the ConsumerRecord-Data is changed:

OUTPUT_CHECK TOPIC_PARTITION: TopicPartition(topic='SAMPLE_TOPIC', partition=0)
BEFORE SUBSCRIPTION - TOPIC: SAMPLE_TOPIC

AFTER SUBSCRIBE - SUBSCRIPTION: {'SAMPLE_TOPIC'}
AFTER SUBSCRIBE - ASSIGNMENT: set()
AFTER SUBSCRIBE - PARTITIONS FOR TOPIC {0, 1, 2, 3, 4, 5, 6, 7}

AFTER OFFSET CHECK - SUBSCRIPTION: {'SAMPLE_TOPIC'}
AFTER OFFSET CHECK - ASSIGNMENT: {TopicPartition(topic='SAMPLE_TOPIC', partition=4),
    TopicPartition(topic='SAMPLE_TOPIC', partition=7), TopicPartition(topic='SAMPLE_TOPIC', partition=0),
    TopicPartition(topic='SAMPLE_TOPIC', partition=6), TopicPartition(topic='SAMPLE_TOPIC', partition=3),
    TopicPartition(topic='SAMPLE_TOPIC', partition=2), TopicPartition(topic='SAMPLE_TOPIC', partition=5),
    TopicPartition(topic='SAMPLE_TOPIC', partition=1)}

ConsumerRecord(topic='SAMPLE_TOPIC', partition=0, offset=1, timestamp=163345635146,
    timestamp_type=0, key=b'SOME_KEY', value=b'SOME AVRO ENCODED MESSAGE', headers=[],
    checksum=None, serialized_key_size=12, serialized_value_size=954, serialized_header_size=-1)

OUTPUT_CHECK TOPIC_PARTITION: TopicPartition(topic='SAMPLE_TOPIC', partition=1)
BEFORE SUBSCRIPTION - TOPIC: SAMPLE_TOPIC

AFTER SUBSCRIBE - SUBSCRIPTION: {'SAMPLE_TOPIC'}
AFTER SUBSCRIBE - ASSIGNMENT: set()
AFTER SUBSCRIBE - PARTITIONS FOR TOPIC {0, 1, 2, 3, 4, 5, 6, 7}

AFTER OFFSET CHECK - SUBSCRIPTION: {'SAMPLE_TOPIC'}
AFTER OFFSET CHECK - ASSIGNMENT: set()
Traceback (most recent call last):
  File "test_executor.py", line 88, in <module>
    main(argument_parsing())
  File "test_executor.py", line 58, in main
    BasicKafka.output_check(con_dict)
  File "...", line ..., in output_check
    msg: ConsumerRecord = read_single_message(kafka, tp, offset)
  File "...", line ..., in read_single_message
    kafka.seek(topic_partition, offset)
  File "/usr/lib/python3.8/site-packages/kafka/consumer/group.py", line 818, in seek
    assert partition in self._subscription.assigned_partitions(), 'Unassigned partition'
AssertionError: Unassigned partition