I am quit sure it is the connected ssd that is the problem. If it is a sandisk extreme portable then it could have been working well for a long time but now going wrong. Read the articles about all sandisk ssd drives of this model and shape have soldering issues causing hardware to fail in the long run.
Actually there are not that many options that work really well and give you enough recording time.
I recently build my own ssd using the Sabrent M.2SSD EC-SNVE usb-type C enclosure with a samsung 2TB 980RPO pcie4.0 NVME M.2 SSD I can say because I have tested it extensively that this works for the atem mini pro iso 50frps highest bitrate with 4 camera's connected and a lot of movement all of the in frames. It also works with the atem mini extreme iso with 8 camera's in 50frps hyperdeck high setting (so actually 9 full quality recordings simultaneous). BlackMagic should update the list of possible SSD that can work with the full use of the ISO all camera recording possibilities but then again that requires a lot of time. Maybe better if more people who actually use the iso recordings to their max limits tell here what ssd they use. Watch this Doug video. It is 1 year old now but it still makes a lot of sense and shows the setup I created after seeing this video. I have to add that at the time of creation there was no news about the failing of the sandisk ssd drives so Doug does recommend that one also in this video but you better not risk that one..

Or a quick look at my 8 camera atem recording setup here:
I first bought the Atem Mini Pro. Later the Extreme Iso. I record theater plays usually with 1 manned + 5 unmanned camera's. I try to create a live mix as much as possible so I only have to correct mistakes in post.