I started a small organization, now small business and am weaseling my way into the hunting industry which is already oversaturated so I have exactly zero room for camera failure. I was just in an out of state hunt in Tennessee when my G50 kept saying "check sd card" so i swapped it for the backup and then the first card was running fine later that afternoon so I used it for the next morning. It is a 256gb Sandisk extreme pro, so it should have the fastest writing speeds they make. Anyways, the next morning I was chasing gobblers running and gunning self-filming, and when a big turkey ran towards me I hit record, it came out on a trail and I took the shot. I saw that the camera said "insufficient writing speeds" then subsequently asked me if i wanted to do a data recovery, and i ended up with 6 seconds of video, and it cut out just before I shot. This costed me more than you probably know, with how difficult it is for everything to go right, and how much it costs me to travel out of state to make great content. I have initialized the card but am uncomfortable with using it again. Any tips on why it may be doing that, if its the camera, the card, or what. I really dont know but this has not happened with any other card and it cannot happen again. My potential dream career depends on it. Thanks!
Based on what you describe it certainly sounds like a writing failure, but not necessarily due to write speed as that would generally produce a different error message indicating a full buffer or a "please wait" message. It is possible the cards are counterfeit and thus not writing at their advertised speeds, but usually the only way to verify that is to check that the seller is an authorized retailer and maybe checking with Sandisk directly. It's not something I'm particularly knowledgable in except that I have heard and read of such instances, Sandisk would likely be able to help determine if this is the case here. But regarding memory cards in general, if you are able to swap cards occasionally you might find a system of more small capacity cards, say four 64GB cards over the one 256GB card, may produce more consistent write speeds and a lower chance of catastrophic failure.
All that aside, if you find the camcorder keeps causing this error across multiple cards, it's probably best to ahve the camcorder examined by a repair technician.
When I ordered my Corvette Z06 back in 2016, I ordered a couple of fast SanDisk SD cards from Amazon to use with its built in system that records HD video along with the data stream from the various vehicle sensors. I had some of the same fast SanDisk SD cards I had bought earlier from B&H and the Amazon sourced cards were clearly counterfeit and I returned them. I learned later that a significant percentage of SanDisk SD and CF cards that were returned under warranty were counterfeit and it is a very highly counterfeited product. I only buy cards from B&H now but other major specialty stores would also be safe.
Does your G50 have dual SD card slots? I think it is a lower cost, close relative of my XF-400 and they have a lot in common. I rarely use the feature but the XF-400 will record to both cards simultaneously and the owners manual states that if one card has an issue in dual recording, the recording will continue on the good card. It sounds like you are recording guided hunts and this is one of the situations where there isn't a "do over" so having the addtional safety of using both card slots makes sense.
You may also decide you don't need 256 GB cards depending upon what you are recording and how much recording room you need before dumping the files to a computer. I don't use my XF-400 in 4K high frame rate mode unless I really need that quality of output and most of the time you don't. A 4K 60 fps video stream creates an very large data file. I use a pair of very powerful HP Z series dual CPU workstations and big video files are still a pain.