Kivy gui lags on raspberry after using timer - python-3.x

Question

I am using kivy 1.10.1 with python 3.4.2 on my raspberry pi 3 and the GUI with some buttons and labels is working fine. Now I want to update the GUI every second to show some new data (update the clock, get some values from database etc.)
The Problem:
When I start the timer the GUI is getting very slow. I tested some modifications of the code like disabling the data reading but without any effect. Everytime the timer is called, the GUI is lagging for some milliseconds.
Does anybody have some idea what's the reason for that? I am sure the hardware of my raspberry is not the problem because when I use the kivy examples (e.g. with some 3D rendering) everything is working without any lags.
Kivy details:
[INFO ] [Kivy ] v1.10.1
[INFO ] [Python ] v3.4.2 (default, Oct 19 2014, 13:31:11)
[GCC 4.9.1]
[INFO ] [Factory ] 194 symbols loaded
[INFO ] [Image ] Providers: img_tex, img_dds, img_sdl2, img_pil, img_gif (img_ffpyplayer ignored)
[INFO ] [Window ] Provider: egl_rpi
[INFO ] [GL ] Using the "OpenGL ES 2" graphics system
[INFO ] [GL ] Backend used <gl>
[INFO ] [GL ] OpenGL version <b'OpenGL ES 2.0'>
[INFO ] [GL ] OpenGL vendor <b'Broadcom'>
[INFO ] [GL ] OpenGL renderer <b'VideoCore IV HW'>
[INFO ] [GL ] OpenGL parsed version: 2, 0
[INFO ] [GL ] Shading version <b'OpenGL ES GLSL ES 1.00'>
[INFO ] [GL ] Texture max size <2048>
[INFO ] [GL ] Texture max units <8>
[INFO ] [Window ] virtual keyboard allowed, multiuser mode, not docked
[INFO ] [Text ] Provider: sdl2
[INFO ] [KivyMD ] KivyMD version: 0.1.2
Code snippet:
# Start timer in a separated thread
def start_timer_gui(self):
try:
# Test connection
if s_conn.test_serial(self) == True:
th = threading.Thread(target=self.thread_timer_gui,
args=())
th.start()
...
# Start timer (is in a separated thread)
def thread_timer_gui(self):
Clock.schedule_interval(partial(self.thread_timer_gui_methods), 1)
#timeit
# Call functions for updating gui from separated thread
def thread_timer_gui_methods(self, dt=0):
self.update_gui()
#self.get_measured_vales()
def update_gui(self):
self.emcstatebar.lbl_local_time.text = "13-03-2019 07:32"
...
I already read infos from this page https://kivy.org/doc/stable/guide/events.html but it didn't help me.
Best regards!

Answer 1

I found a solution. If is just update GUI elements with "schedule_interval(...)" everything is working fine. The lag occurs if I try to get measured values via "schedule_interval(...)". I changed getting values to a seperate thread with:
# Get measured values in a separated thread)
def thread_timer_values(self):
while True:
self.get_measured_vales()
time.sleep(2)
Now I can show measured values in GUI without lag!