No major issues - just differences that may matter for some people.
- The A1 reduces EVF resolution and reduces EVF refresh with high speed photography in continuous mode.
- The EVF is not as bright as the Z9 - relevant for bright outdoor conditions
- The buffer is large, but buffer clearing is slow; this has an especially large impact in backup mode writing to two cards.
- CFExpress Type A is a little slower and harder to find than Type B used by Canon and Nikon.
- Limited RAW file options create a very large amount of data with high frame rates. Nikon's High Efficiency RAW is a viable option.
- Requires additional grip and battery for extended shooting.
- Potential for overheating / limited weather sealing with 8k for extended periods prevents 8k 60p (it does have 4k 60p).
- Limited output options for ProRes RAW video (requires Atmos while Z9 does not require an external recorder).
- AF subject identification somewhat limited to eyes but not other subjects (aircraft and vehicles).
- AF struggles with Face/Eye AF for backlit subjects (a problem area for most cameras and an area that will improve).
- Lacks AF Eye Control found in Canon R3.
- Lack of full size HDMI output found on Z9.
- Fastest shutter speed slower than 1/32,000 sec of Z9.
- Slowest shutter speed setting less than 900 seconds (15 minutes) for Z9.
- Shorter battery life / lower voltage to power lenses and accessories at highest speed
- Significantly higher cost (about $1700+) - especially when considering a grip and additional batteries.
You can pick any flagship camera and come up with a list of potential shortcomings, and even then some of those issues may only occur under certain circumstances. It's not a fault of the A1 - just later cameras play a game of leapfrog by adding new features and capabilities. I don't think any of these items would justify switching systems for most people - but there are shortcomings that may require workarounds or limit capabilities.