In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is on course to record a decent gain. At the time of writing, the benchmark index is up 0.65% to 7,970.8 points.

Four ASX shares that have failed to follow the market higher today are listed below. Here's why they are falling:

DroneShield Ltd (ASX: DRO)

The DroneShield share price is down 3% to $1.17. This may have been driven by profit taking after some strong gains from the counter drone technology company's shares this month. One broker that is likely to see today's pullback as a buying opportunity is Bell Potter. This morning, it reaffirmed its buy rating with an improved price target of $1.50. The broker said: "DroneShield remains our key pick in the Defence sector, with macro tailwinds driving increasing customer demand and the company well capitalised to fund further R&D to maintain its market leading position. We retain our BUY recommendation."

Generation Development Group Ltd (ASX: GDG)

The Generation Development share price is down almost 17% to $4.04. Investors have been selling this financial services company's shares following the release of a market update. The company notes that it delivered a strong performance in the March quarter, with all businesses contributing to growth despite continued market volatility. It seems that the market was expecting an even stronger performance. In addition, today was supposed to be a big day for the company with its shares joining the ASX 200 index to replace De Grey Mining Ltd (ASX: DEG).

Oneview Healthcare PLC (ASX: ONE)

The Oneview Healthcare share price is down 5% to 27.5 cents. This has been driven by the release of the Ireland based healthcare technology company's quarterly update. During the quarter, the company recorded cash receipts of 4.2 million euros but an operating cash outflow of 1.25 million euros. This meant that Oneview ended the period with a cash balance of 12.2 million euros.

PWR Holdings Ltd (ASX: PWH)

The PWR share price is down 7% to $6.21. This has been driven by news that auto part's founder and managing director, Kees Weel, is stepping back from the role temporarily. According to the release, this is so that Weel can seek treatment for an acute medical condition. Chief Technical and Commercial Officer Matthew Bryson will be acting CEO in his absence. Weel said: "While I will remain active in PWR's overall direction, I have advised the Board that concentrating on my recovery is my priority. Matthew Bryson and the Executive Leadership Team have my full support, and I have complete faith that they will be able to deliver on PWR's objectives and the move to PWR's new headquarters, which has successfully commenced."