When you rename a chest, placing two together doesn't make a large chest but 2 normal sized chests.
MCPE-17286
Chest Combining
Resolved
Duplicate
0
Thank you for your report. This issue was, however, submitted earlier as MCPE-16216. Please perform a search next time to make sure your bug hasn't already been reported. The parent issue can easily be found by searching for "mcpe unresolved rename chest".