I installed an Ethernet patch cable, and after the connection was completed, I used a tester to check it. However, the lights on the RJ45 tester were not flashing correctly. Does anyone know why this happened, and what can I do to resolve it??? 
In my personal operating experience, the probability of such a problem, as you expressed, is that you made a mistake in wiring. When the RJ45 connector is made correctly, the lights on both sides of the cable will light up from 1-8. If the lights come on in the wrong order, then you have made the bad RJ45 connector. Please judge which RJ45 connector you have made is faulty according to the light-up situation.
- Operation instructions:
(1) Insert a 9V battery.
(2) Insert the two ends of the cable you want to test into the main unit and remote unit, ensuring a secure connection.
(3) Switch on the power to perform a quick scan test (S for slow scan mode). The main tester and remote tester lights up in sequence for 1, 2, 3, 4, 5, 6, 7, 8, G, indicating that the wire ends are good. The G light will not light up if testing unshielded cables.
(4) If multiple wires are short-circuited, the corresponding lights on both testers will not light up.
(5) If multiple cables are not connected (3 or more), all indicator lights will not light up.
(6) If the cable ends are crossed, for example, wires 4 and 5 are switched, it will display:
Main tester: 1-2-3-4-5-6-7-8-G
Remote tester: 1-2-3-5-4-6-7-8-G
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Usually, this happens when your RJ45 plug isn’t plugged in properly. You may need to redo the RJ45 connection.
you should check your battery
Firstly, you should check if your RJ45 tester can work well. For example, if your tester is not used for a long time, it can have some problems.
The next thing is that you should ensure you have correctly terminated the network cable. If more than 3 wires are not well connected, the tester will also not flash.
If this tester tests the other cables is OK, there must be something wrong with your connection, maybe a short circuit or open circuit