The game comes to a grinding halt whenever it begins to autosave, which is very frequent. Blocks refuse to render, mined blocks refuse to disappear, and the game's frame rate drops, and begins to lag horribly during this process. It's especially noticeable when playing online with friends, or splitsceen multiplayer.
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Another data point for the devs, it seems to be worse depending on how full the system memory is. While riding close to full (after downloading Smash Ultimate, a whopping 15GB!) the lag was very frequent and long lasting. After archiving Smash and moving to an SD card, the lag/freeze duration while autosaving has gone down considerably, yet they still occur pretty often.
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I can confirm this issue too. Specially in splitscreen multiplayer the game experience gets very affected. I created a similar bug report MCPE-40976 hoping the devs can see this problem that affects so much to some of us.
Auldrick
Thank you for your report!
We're actually already tracking this issue at MCPE-34910, so we will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Can confirm this issue. It's gotten worse on each update. The problem occurs on auto save, and is worse the more local players you have (hardly ever see the issue with only one player, and the lag/freeze lasts the longest with all 4 players playing.