If a time series has random time events, how to detect patterns? My app receives messages with a random number of bits at a random time. But two weeks ago I started to notice some almost regular patterns on the metrics of my app. I suspect they are some bots sending artificially generated data to my app. Specifically, I'm looking for sequential subsets of messages in a time series where messages has almost the same number of bits.

I read about some methods but they use data where time is not a random variable. I appreciate any help you can provide, including books, web pages, tutorials (in Python if possible), etc.
As a first step, to segregate the messages that appear to be a bot, you could first try binning by message size. For example, if messages sent by bots are likely to be around 128 bytes to 140 bytes, assign these to a unique bin.

Next, create a time series based on this bin. Try to decompose the time series using an additive or multiplicative method such as Holt Winters. A strong seasonal component would help you identify regular and repetitive messages which are being generated automatically.