Varnish Issue

Recently I configured Varnish on my blog https://www.bloggingcage.com/

On front end it is working awesome but when I am trying top open any post it is downloading one file automatically.

When I opened the file it has –

<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require( dirname( __FILE__ ) . '/wp-blog-header.php' );

How to solve this issue?

Here are my logs
81 0.00 inf backend_busy – Backend conn. too many
72 0.00 inf backend_reuse – Backend conn. reuses
13 0.00 inf backend_toolate – Backend conn. was closed
33 0.00 inf backend_retry – Backend conn. retry
25 0.00 inf fetch_head – Fetch head
34 0.00 inf fetch_bad – Fetch had bad headers
24 0.00 inf fetch_close – Fetch wanted close
59 0.00 inf fetch_oldhttp – Fetch pre HTTP/1.1 closed
59 0.00 inf fetch_1xx – Fetch no body (1xx)
13 . . n_wrk – N worker threads
1 0.00 inf n_wrk_create – N worker threads created
13 0.00 inf n_wrk_failed – N worker threads not created
13 0.00 inf n_wrk_lqueue – work request queue length
30 0.00 inf n_wrk_queued – N queued work requests
2 0.00 inf n_wrk_drop – N dropped work requests
1 . . n_backend – N backends
10 . . n_expired – N expired objects
10 . . n_lru_nuked – N LRU nuked objects
1 0.00 inf s_sess – Total Sessions
20 0.00 inf s_req – Total Requests
10 0.00 inf s_pass – Total pass
63 0.00 inf s_bodybytes – Total body bytes
81 0.00 inf sess_pipeline – Session Pipeline
72 0.00 inf sess_readahead – Session Read Ahead
26 0.00 inf sess_herd – Session herd
59 0.00 inf shm_records – SHM records
26193 0.00 inf shm_writes – SHM writes
285224 0.00 inf shm_flushes – SHM flushes due to overflow
19 0.00 inf shm_cont – SHM MTX contention
57 . . sms_nobj – SMS outstanding allocations
69 . . sms_nbytes – SMS outstanding bytes
5793 . . sms_balloc – SMS bytes allocated
802 . . sms_bfree – SMS bytes freed
59 0.00 inf n_ban_re_test – N regexps tested against
1 0.00 inf n_ban_dups – N duplicate bans removed
1 0.00 inf hcb_nolock – HCB Lookups without lock
1 0.00 inf hcb_insert – HCB Inserts
1 0.00 inf esi_errors – ESI parse errors (unlock)
1 0.00 inf esi_warnings – ESI parse warnings (unlock)