Printer gets slow down during printing

I am using hypercube 3d printer, 12v SMPS , BTT SKR V1.4 motherboard along with A4988 stepper driver and nema 17 motors.

Currently I am facing following two issues:

1) while printing, my printer gets slowdown arbitrary at many places and in those layers, material get diposit more, and several blob appears.
What is the reason for slowing down the nozzle while printing and what shall I do?

2) sometimes while printing, hotend thermistor shows drop in nozzle temperature and when this drop in temperature goes beyond 4-5 degree Celsius, my printer beeps and gives me error of "Thermal Runaway E1"
This don't happens to every print.
I am unable to figure out the reason for this unusual behaviour. If I heat the nozzle to a desired temperature without giving any print, that time it is not giving me any error.
What could be the reason for this ?

Kindly respond at the earliest. Waiting for your response

Thank you

1) if the original model is stupidly detailed all the tiny segments will slow down a printer. you need to reduce the size of the mesh

2) the most common cause is the cooling fans blowing on the hot end instead of cooling fins or extruded plastic.

Sorry but I haven't got you completely

1) what do you mean by stupidly detailed ? How to reduce mesh size.
2) I am using hotend cooling fan as well as part colling fan. Part colling fan duct is just 5-10 mm away from nozzle. And hotend colling fan lies on the hotend fins.

I am printing lithophanes, so how can I adjust mesh size in that ?
Kindly respond

Please respond me!

1)I am printing lithophanes, I increased my retraction from 6.5 mm to 7.5 mm still little zits/blobs can be seen on the surface of lithophanes.

2) I am using pronterface for printing, My printer gets slow down at some layers while printing . When it's slow downs, I just click the button of mouse randomly on pronterface interface then printing speed becomes normal. I don't think this is mesh size issue. What could be the reason for this?

3) sometimes my printer stops printing, I feels this is because of temperature drop and printer beeps. When I heat the nozzle at 205 deg cel. without printing anything that time it heats up to that temperature without giving any error and stay stable there without any temperature drop.
But when I give print, after few layers of printing temperature drops from 205 deg.cel. to 200 deg. Cel.. Printer gives me heating error and it stops printing. ( This do not happen to all the prints, for some prints temperature drops for 4 deg.cel and then again increases and gets stable at 205deg.cel)
What could be the reason for this?

Please respond.waiting for your support.

Thanks and regards,

1: Presumably you are using a Bowden setup. Long retractions might be a result of loose fitting of the filament inside the Bowden tube. Some tubes (e.g. Capricorn) are a better fit than most others. They might also result from looseness of the fittings at either end of the tube.
Perhaps try faster retraction rather than longer retraction.

2: I expect that using Proterface means that the communication between computer and printer is via USB. Works OK, but is often slowed down by the computer for reasons that only the computer knows! Reading a file from an SD card or a USB stick is often more reliable because it is not at the whim of a computer.

3: In general it is not always easy to avoid the part fan blowing on the hotend, but that is what you should aim for. Do you have an insulating silicone sock on the hotend? If not, then that might fix your problem. If an appropriate sock is not available then you can hack an alternative using high temperature silicone or fibreglass and Kapton tape. I used the fibreglass and tape solution for quite a while.
Perhaps you could ramp up the fan rate gradually over a few layers so that the hotend heater can more nearly keep the temperature constant so that the heater failure detection is not triggered.