When I try to connect two structures at an angle, for example a straight section and an euler bend (to form a loop mirror) then there is an offset ,which is within the database unit but is there. If there is no angle then this seems to go away (see the attachment). However this is not an isolated example, sometimes even structures without an angle seems to have this offset. I agree this won’t affect the fabrication but it will be good if we can avoid it.
I can’t see the attachment, but I assume that you refer to the small (< 1 dbu) gaps. These cannot be avoided, because they are inherent to the integer rounding in GDS. See these two posts for a discussion: