This Bug was originally discovered by @skrausse , thank you for reporting.

Describe the bug
When trying to use the delete_synchrofacts method from Synchrotool class in spike_train_synchrony.py, in specific cases an IndexError is raised.

To Reproduce

1. Install elephant and neo
2. Run the following minimal example:

# fix synchrotool
import elephant, neo
import quantities as pq
from elephant import spike_train_synchrony


import elephant.spike_train_generation as stg
import numpy as np

np.random.seed(1)  # set random seed 2 for no error

SPP = stg.StationaryPoissonProcess(50 * pq.Hz, t_start=0 * pq.ms,
                                   t_stop=1000*pq.ms)
test_sts = SPP.generate_n_spiketrains(2)

sampling_rate = 30000*pq.Hz
test_obj = spike_train_synchrony.Synchrotool(
    test_sts, sampling_rate=sampling_rate, spread=2)
test_obj.delete_synchrofacts(threshold=2, in_place=True)

Gives the following error messages: (if np.random.seed(1), if the random seed is set to 2 , no error is raised)

Traceback (most recent call last):
    test_obj.delete_synchrofacts(threshold=2, in_place=True)
  elephant/spike_train_synchrony.py", line 325, in delete_synchrofacts
    self.annotate_synchrofacts()
  elephant/spike_train_synchrony.py", line 407, in annotate_synchrofacts
    complexity_per_spike = epoch_complexities[spike_to_epoch_idx]
IndexError: index 91 is out of bounds for axis 0 with size 91

Expected behavior
Index should not be out of bounds

Environment

• OS (e.g., Linux):Ubuntu 20.04.4 LTS (64-bit)
• How you installed elephant (conda, pip, source): pip, source
• Python version: 3.8
• neo python package version: 0.10.2
• elephant python package version: 0.11.0
• quantities: 0.13.0
• numpy: 1.22.3