In my experience using DeepSeek v4 Flash free tier (context size limited to ~200k), the model isn't nearly as good as the paid one for agentic coding tasks. Unsure, if that's the case with these other providers too, though I wouldn't be surprised if it indeed is.
There is no official dsv4 flash free tier api afaik. Did you get it from open router or something? Likely quantized.
The paid official dsv4 api already shares data with deepseek for training