In 2014, Springer and IEEE had to retract 120 comp-sci papers that were gibberish generated with SCIgen. The problem persists as of May 2021[1], and given the advancements in LLMs, I wouldn't be surprised if things are getting worse...
[1] https://asistdl.onlinelibrary.wiley.com/doi/10.1002/asi.2449...