Website fails to connect

Likely problem is what you're calling Backup DNS Servers.

These servers should only be caching servers, so your internal lookups match your external lookups.

Be sure you have forwarders setup to either global root servers or better Google's stable servers, which are 8.8.8.8 + 8.8.4.4 + tend to always be up.

Follow becraig's advice. Run an nslookup for your domain explicitly pointing to 8.8.8.8 + then both your Backup DNS Servers.

If there's any difference between what Google (8.8.8.8) returns + your Backup DNS Servers, then best fix this broken config.

A"Likely problem is what you're calling Backup DNS Servers." --> OK. I will start working on it this evening and report back.

Follow becraig's suggestion.

The nslookup tool can surface problems instantly.

Sorry about late reply.
In internet browser, https://www.kuebix.com home page shows up after several minutes of delay in broken parts as seen in the screenshot.

Here are results of NSLOOKUP and TRACERT:

(1) nslookup kuebix.com

C:\Users\User>nslookup kuebix.com
Server:  DC1.DC.local
Address:  192.168.1.9

Name:    kuebix.com
Address:  35.185.248.37

(2) Tracert

C:\Users\User>Tracert 35.185.248.37

racing route to 37.248.185.35.bc.googleusercontent.com [35.185.248.37]
ver a maximum of 30 hops:

 1     3 ms     1 ms     1 ms  192.168.1.1
 2     *        *        *     Request timed out.
 3    15 ms    24 ms    19 ms  dynamic-76-73-172-225.knology.net [76.73.172.225

 4    21 ms    17 ms    12 ms  76-73-167-196.knology.net [76.73.167.196]
 5    15 ms    18 ms    12 ms  76-73-167-201.knology.net [76.73.167.201]
 6    11 ms    15 ms    10 ms  76-73-167-198.knology.net [76.73.167.198]
 7    17 ms    12 ms    11 ms  76-73-166-126.knology.net [76.73.166.126]
 8    13 ms    13 ms    12 ms  76-73-166-125.knology.net [76.73.166.125]
 9    26 ms    22 ms    22 ms  user-24-214-131-160.knology.net [24.214.131.160]

10    31 ms    20 ms    21 ms  static-76-73-191-226.knology.net [76.73.191.226]

11    24 ms    23 ms    26 ms  206.41.110.37
12    23 ms    24 ms    24 ms  108.170.243.197
13    35 ms    23 ms    25 ms  72.14.232.109
14    32 ms    34 ms    38 ms  72.14.232.70
15    44 ms    42 ms    49 ms  209.85.251.139
16    76 ms    83 ms    74 ms  216.239.49.135
17    77 ms    75 ms    74 ms  216.239.46.175
18     *        *        *     Request timed out.
19     *        *        *     Request timed out.
20     *        *        *     Request timed out.
21     *        *        *     Request timed out.
22     *        *        *     Request timed out.
23     *        *        *     Request timed out.
24     *        *        *     Request timed out.
25     *        *        *     Request timed out.
26     *        *        *     Request timed out.
27    95 ms    77 ms    75 ms  37.248.185.35.bc.googleusercontent.com [35.185.248.37]

Trace complete.

@Atlas
WOW (Wide Open West) is my ISP. I have Cisco router, but I do not have firewall. The strange thing is that this is only website with problem and there are 15 users surfing the internet daily. If firewall or ISP is problem, then shouldn’t we experience the same issue on other websites?
I do not know what the wire shark is or does. Can you provide URL?

I'd also suggest getting fiddler from fiddlertool.com
Install it in a machine that cannot access the site.
Once installed start monitoring browser traffic and share the logs or even a screenshot of the results.

"Install it in a machine that cannot access the site." --> I will install it on a PC, but the problem with the site is happening to ALL computers on the network.

WOW and knology are same thing.

Wire shark is a packet sniffer.

And not necessarily across all websites.  May be something particular to docs.

Pull the wire shark capture and let's have a look.

@BeCraig
I installed Fiddler and things are scrolling up busily on the left window pane. What am I supposed to do here?

How do I set this up?

I found the problem.
In Cisco router configuration, I created BLOCK LIST where I block certain IP addresses using DENY command like below:
deny ip 5.0.0.0 0.255.255.255 any
deny ip 31.0.0.0 0.255.255.255 any
.... etc

This cause some websites located overseas (southest Asia and Latin America) being blocked when users try to visit a couple of websites.
After this BLOCK LIST was removed, the problem is solved.
I will have to be more specific with IP addresses in my BLOCKLIST.

Thanks you all for your help.