We also see some similar reports every day in the "ERROR" log (some examples below), I'd be curious to know what they are referring to...
Examples:
[2025.05.03] 10:23:07.964 [MAIL SERVICE] The given key '4794' was not present in the dictionary.
[2025.05.03] 10:23:59.284 [MAIL SERVICE] The given key '3120' was not present in the dictionary.
[2025.05.03] [MAIL SERVICE] The given key '3121' was not present in the dictionary. at System.Collections.Concurrent.ConcurrentDictionary`2.ThrowKeyNotFoundException(TKey key)
[2025.05.05] 10:16:48.108 [MAIL SERVICE] The given key '42411' was not present in the dictionary.
[2025.05.05] 16:31:55.448 [MAIL SERVICE] The given key '740' was not present in the dictionary.
[2025.05.05] [MAIL SERVICE] The given key '743' was not present in the dictionary. at System.Collections.Concurrent.ConcurrentDictionary`2.ThrowKeyNotFoundException(TKey key)
[2025.05.06] 09:25:35.015 [MAIL SERVICE] The given key '937' was not present in the dictionary.
[2025.05.06] 10:24:04.727 [MAIL SERVICE] The given key '3161' was not present in the dictionary.
[2025.05.07] 12:07:37.208 [MAIL SERVICE] The given key '5687' was not present in the dictionary.
[2025.05.08] 14:13:36.622 [MAIL SERVICE] The given key '4890' was not present in the dictionary.
[2025.05.11] 09:49:43.139 [MAIL SERVICE] The given key '4945' was not present in the dictionary.
[2025.05.11] [MAIL SERVICE] The given key '4952' was not present in the dictionary. at System.Collections.Concurrent.ConcurrentDictionary`2.ThrowKeyNotFoundException(TKey key)
[2025.05.12] 07:54:27.351 [MAIL SERVICE] The given key '4960' was not present in the dictionary.
[2025.05.12] 07:54:46.563 [MAIL SERVICE] The given key '3532' was not present in the dictionary.