Cannot connect to a specific Minecraft server using router/modem

Question

I'm having trouble connecting to one specific Minecraft server through my home internet. I've tried to connect using 2 separate PC's (one using a wired connection and the other wireless) with no luck. However, I can connect to the server using a mobile hotspot, which confirms that I'm using the right Minecraft version (1.14.3) and IP address. I'm also able to connect to multiple other servers, it's just this particular one I'm having trouble with. No other players on the server have had any problems connecting.

All this leads me to believe that the problem lies with my router/modem configuration. I'm using a Sagemcom Gateway F@ST3864V2.

I don't have much knowledge when it comes to router settings, so any advice as to what may be causing this issue or which settings I should tinker with would be greatly appreciated!

Update #1:

Here's the log from when I try to connect to the server:

[19:49:01] [Client thread/INFO]: Connecting to <ip>, 25565
[19:49:01] [Server Connector #1/ERROR]: Couldn't connect to server
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.String.charAt(String.java:646) ~[?:1.8.0_51]
    at io.netty.bootstrap.Bootstrap.isBlockedServer(Bootstrap.java:383) ~[patchy-1.1.jar:?]
    at io.netty.bootstrap.Bootstrap.checkAddress(Bootstrap.java:364) ~[patchy-1.1.jar:?]
    at io.netty.bootstrap.Bootstrap.doResolveAndConnect(Bootstrap.java:180) ~[patchy-1.1.jar:?]
    at io.netty.bootstrap.Bootstrap.connect(Bootstrap.java:162) ~[patchy-1.1.jar:?]
    at io.netty.bootstrap.Bootstrap.connect(Bootstrap.java:150) ~[patchy-1.1.jar:?]
    at jb.a(SourceFile:318) ~[1.14.3.jar:?]
    at cza$1.run(SourceFile:66) [1.14.3.jar:?]

I can ping the server IP through a terminal without any problems:

Pinging <ip> with 32 bytes of data:
Reply from <ip>: bytes=32 time=223ms TTL=51
Reply from <ip>: bytes=32 time=223ms TTL=51
Reply from <ip>: bytes=32 time=223ms TTL=51
Reply from <ip>: bytes=32 time=222ms TTL=51

Ping statistics for <ip>:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 222ms, Maximum = 223ms, Average = 222ms

A trace route is also successful:

Tracing route to <ip> over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  192.168.0.1
  2     6 ms     6 ms     6 ms  1.42.0.1
  3     *        *        *     Request timed out.
  4     6 ms     5 ms     5 ms  198.142.249.242
  5   160 ms   160 ms   160 ms  203.208.131.205
  6   161 ms   163 ms   166 ms  62.115.8.202
  7   223 ms   223 ms   233 ms  62.115.114.87
  8   214 ms   214 ms     *     62.115.141.245
  9   223 ms   223 ms   223 ms  80.91.246.36
 10   223 ms   223 ms   223 ms  62.115.145.91
 11     *        *        *     Request timed out.
 12     *        *        *     Request timed out.
 13     *        *        *     Request timed out.
 14   222 ms   223 ms   223 ms  <ip>

Trace complete.

Answer 1

I managed to solve this issue by setting a static IP address for my PC.

Edit:

The steps involved were googling 'Setting a static IP address Windows 10' and then following this tutorial exactly.