It happens since each mobile device and WhatsApp version has it's own way of storing the chats. You can open a new issue on the GitHub repository and share a small piece of chat (if possible) so that the viewer can be updated according to the formatting of your device and WhatsApp version.
Do mention your WhatsApp version, mobile OS and device name for better tracking.

Your WhatsApp chats are automatically backed up and saved daily to your phone's memory. Depending on your settings, you can also periodically backup your WhatsApp chats to Google Drive. If you uninstall WhatsApp from your phone, but don't want to lose any of your messages, be sure to manually back up your chats before uninstalling. To backup your chats, go to WhatsApp > Menu Button > Settings > Chats > Chat backup > Back Up.

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Read More: https://faq.whatsapp.com/en/android/23756533

Your WhatsApp messages are automatically backed up and saved daily to your phone's memory. Depending on your settings, you can also periodically back up your WhatsApp chats to OneDrive. If you uninstall WhatsApp from your phone, but don't want to lose any of your messages, be sure to manually back up or export your chats before uninstalling.

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Read More: https://faq.whatsapp.com/en/wp/22548236

No.
Your chat gets deleted as soon as you upload the file. You can feel safe on that front.

No.
Since your chat is getting deleted as soon as you upload the File, you cannot preserve your chat history for you to visit later.