Shares of software company, Appen (ASX:APX), fell sharply by as much as 21.3% to A$0.850, its biggest intraday percentage loss since January.

The plummet in shares came about after Appen received a proposal for an all-stock deal offer from U.S.-based digital data solutions company, Innodata.

Innodata’s buyout offer was valued at A$0.70 per Appen share, which was significantly below the company’s closing price of A$1.08 on the previous Tuesday.

Notably, Appen shares soared by as much as 40% on that Tuesday before trading was momentarily halted due to an unexpected movement in share price.

A total of more than 13.8 million shares were traded compared to the 30-day average volume of about 7.7 million shares.

Despite the tumultuous day, Appen’s stock has gone up by 71.4% this year, prior to the last close, far outperforming the 1.6% increase in the benchmark S&P/ASX 200 index.

Appen is a global software company that is largely known for its development of high-quality, human-annotated datasets for machine learning and artificial intelligence.