Just before midday, bourse operator ASX was still working to resolve the issue, which began after 9am.
The S&P/ASX200 was down 17.9 points, or 0.21 per cent, to 8,595, by midday as the broader All Ordinaries lost 23.9 points, or 0.27 per cent, to 8,894.8.
The weak start to the month of December followed the bourse's worst month since March.
"Share markets are bidding farewell to 'pump and dump' November," Moomoo market strategist Jessica Amir said.
In November, ASX200 fell three per cent, the Commonwealth Bank dropped 11.2 per cent, and in the US the tech heavy Nasdaq-100 index declined 1.6 per cent as chip maker Nvidia slid 12.6 per cent.
"These moves were driven by yo-yo expectations of a US rate cut and hotter-than-expected inflation in Australia," Ms Amir said.
But there's a chance the Australian and US markets could stabilise, depending on the outcomes of key US inflation data ahead of a US central bank meeting and Australia's upcoming economic growth report for the third quarter.
Six of 11 local sectors were trading lower by lunchtime, led by a 1.3 per cent dip in health care stocks, which ran into profit-taking after a seven-session winning streak off the recent lows.
Ramsay Health Care bucked the broader sector slump to lift 0.9 per cent, as names like CSL, Sigma, Pro Medicus and ResMed tumbled between one and two per cent.
The heavyweight financials sector grinded 0.4 per cent lower, with CBA the only big four bank with its head above water, up 0.2 per cent to $152.84, while ANZ (-0.9 per cent) led the other three lower.
Raw materials were trading just below flat by midday, with a mixed performance from large cap miners as iron ore futures continued to slip, after factory activity in China slumped for another month, their longest slowdown on record.
Gold stocks were largely lower, although Northern Star managed a 0.9 per cent improvement as the gold price edged higher to around $US4,228 an ounce, on par with November highs.
Lithium miners fell after a strong performance in November, with Liontown shedding two per cent and Pilbara Minerals down 2.7 per cent to $3.94.
Energy stocks edged 0.1 per cent higher as oil prices continued to consolidate in its recent range, following news OPEC+ member countries agreed to keep production targets unchanged in the first quarter of 2026.
Consumer staples grinded 0.2 per cent lower, as Penfolds owner Treasury wines announced $687 million in goodwill writedowns in its US business, prompting a 2.2 per cent sell-off to $5.70.
Wholesale giant Metcash, which narrowly lifted its first-half post-tax profit to $142.2 million and announced an 8.5 cent dividend for shareholders, is in a trading halt while the exchange sorts out the outage issue.
Real estate stocks outperformed the broader market, up 0.9 per cent by lunchtime, led by a two per cent boost to Goodman Group.
The Australian dollar is buying 65.44 US cents, up from 65.29 US cents on Friday at 5pm.
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