If any user use a Child node frontend then its last 5 visited pages always are changing and user's record in the "user_history" table is always changes.
The table "user_history" is synchronized as part of configuration.

The data transmitted for every user is:
user_history.200200000000001.0.title1.1.535f44415348424f415244.url1.1.64617368626f6172642e706870.title2.1.535f435553544f4d5f475241504853.url2.1.6368617274732e7068703f686f737469643d3230303230303030303031303031372667726f757069643d3026677261706869643d323030313030303030303030303035.title3.1.535f4c41544553545f44415441.url3.1.6c61746573742e7068703f67726f757069643d3026686f737469643d3230303230303030303031303031372673656c6563743d266f70656e3d31266170706c69636174696f6e69643d323030313030303030303030303032.title4.1.535f484953544f5259.url4.1.686973746f72792e7068703f6974656d69645b305d3d32303031303030303030303030343026706572696f643d37323030267374696d653d323031313132333031363536333426616374696f6e3d73686f776772617068.title5.1.535f484f535453.url5.1.686f7374732e7068703f67726f757069643d30

for single user it's ~870 bytes
Note: the configuration is synchronized every 130 second

Question: why need to synchronize that data to master node(s)?
I do not see any sense of that.
I suggest to remove flag "ZBX_SYNC" for the table "user_history"

I do not expect here noticeable performance improvement, it's just logical improvement.