"transparent" ground

hi all, before 2.3.1 sometimes i got in some parts or when i played on party saw parts of the ground black and transparent but only for few periods of time. now in all the areas i have most of the instances with that transparent ground. here an example



my pc specifications: amd 2.5GHZ quad core, video card gtx 520 1 gb, 4 gb memory ram, playing on resolution 1904 x 1002 (custom). i reduce texture quality and other visula effect a lot.

hope you can help me, is so tedius to play in group with that effect cause reduce my fps and increase my latency.

regards