sudden reduction of sdram from 1024mb to 512mb

my head unit is a gs version with rk3066 cpu, with 1024mb ram.its about a year i installed it.recently,in about 3-4 wks ago,I noticed the unit is kind of very slow compare to when it was installed and it also hangs with no response too often.This made me to check the unit settings and i discovered the ram size has reduded from 1024 mb to 512mb.has anyone experience this issue before? and if there is any solution to return it to its original 1024 mb.
Thank You.

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