Is there any scriptures says some reasons for someone falling down from spiritual life?
There are different kinds of reasons for a individual to fall off or wander away from the spiritual path /life at the different stages.
The main reasons of falling are either internal (our mind) or External (materialistic world.) The internal reasons are which are generated by our mind like Ego , ignorance , false knowledge , low self-control etc. where as the external reasons are worldly desires , various dukhas (sorrows).
A sadhak or follower of spiritual path faces the danger of falling off the spiritual path, by giving up the integrity, honesty, courage, simplicity and truthfulness ,moral practices , non-attachment to desires , steady spiritual exercises which are most essential for sadhana. So in other words he must maintain the the purity of mind and body , good tendencies throughout his spiritual life.
And it is for this same reason the Mundaka Upanishad says that – .the path of spirituality is not for the weak, but for the brave and the strong willed; because only such people are equipped to overcome all odds and reach the door of their Atman and realize its oneness with Brahman .
नायमात्मा बलहीनेन लभ्यो न च प्रमादात्तपसो वाप्यलिङ्गात् ।
एतैरुपायैर्यतते यस्तु विद्वांस्तस्यैष आत्मा विशते ब्रह्मधाम ॥ 3.2.4॥
nāyamātmā balahīnena labhyo na ca pramādāttapaso vāpyaliṅgāt |
etairupāyairyatate yastu vidvāṃstasyaiṣa ātmā viśate brahmadhāma || 4 ||
This Atman cannot he attained by one devoid of strength or by excitement or by tapas devoid of linga. But of the knower who strives with these aids, the Atman enters into the Brahman.
In his Yoga-Sutras - Verse 1.30-1.32 Maharshi Patanjalii is describing various distractions a Yogi faces during his Sadhana or Spiritual practice of Yoga. They are Sickness, mental laziness, doubt, lack of enthusiasm, sloth, craving for sense-pleasure, false perception, despair caused by failure to concentrate and unsteadiness. So a spiritual aspirant should steadily try to take care of all above conditions otherwise he will not be successful in achieving his goals as well as in his spiritual path and will fail.
व्याधि स्त्यान संशय प्रमादालस्याविरति भ्रान्तिदर्शनालब्धभूमिकत्वानवस्थितत्वानि चित्तविक्षेपाः ते अन्तरायाः ॥३०॥
vyādhi styāna saṃśaya pramāda-ālasya-avirati bhrāntidarśana-alabdha-bhūmikatva-anavasthitatvāni citta-vikṣepāḥ te antarāyāḥ ||30||
Sickness, mental laziness, doubt, lack of enthusiasm, sloth, craving for sense-pleasure, false perception, despair caused by failure to concentrate and unsteadiness in concentration: these distractions are the obstacles to knowledge.
Nine kinds of distractions come that are obstacles naturally encountered on the path, and are physical illness, tendency of the mind to not work efficiently, doubt or indecision, lack of attention to pursuing the means of samadhi, laziness in mind and body, failure to regulate the desire for worldly objects, incorrect assumptions or thinking, failing to attain stages of the practice, and instability in maintaining a level of practice once attained. (vyadhi styana samshaya pramada alasya avirati bhranti-darshana alabdha-bhumikatva anavasthitatva chitta vikshepa te antarayah). So mental weaknesses. even disease is harmful to the follower of spiritual path and lead him to his fall.
This upanishadic mantra from The Isha Upanishad , tells us a follower will fail from his path of spirituality , if he only narrow mindedly is following only single path (one direction only ) either of meditation or karma.i.e Vidya Or Avidya.
अन्धं तमः प्रविशन्ति येऽविद्याम् उपासते ।
ततो भूय इव ते तमो य उविद्यायां रताः ॥ 9 ॥
andhaṃ tamaḥ praviśanti ye'vidyām upāsate |
tato bhūya iva te tamo ya uvidyāyāṃ ratāḥ || 9 ||
Into blinding darkness pass they who adhere to karma and into still greater darkness, as it were, they who delight in meditation.
There is interesting story of Rishi Saubhari's fall down from spiritual path by enjoyed sense gratification in the material world. And later realising that. In Shreemad Bhagvat Purana - Skanda 9-Chapter 6. -SB 9.6: The Downfall of Saubhari Muni.
अहो इमं पश्यत मे विनाशं तपस्विनः सच्चरितव्रतस्य ।
अन्तर्जले वारिचरप्रसङ्गात् प्रच्यावितं ब्रह्म चिरं धृतं यत् ॥ SB 9.6.50 ॥
aho imaḿ paśyata me vināśaḿ tapasvinaḥ sac-carita-vratasya
antarjale vāri-cara-prasańgāt pracyāvitaḿ brahma ciraḿ dhṛtaḿ yat
Alas! While practicing austerity, even within the depths of the water, and while observing all the rules and regulations practiced by saintly persons, I lost the results of my long austerities simply by association with the sexual affairs of fish. Everyone should observe this fall down and learn from it.
There are some different reasons also like unable to overcome Maya , unable to overcome dvaita feeling , not getting a capable Guru to inspire of guide one through spiritual path etc. But as said in above comment by @Rickross they also can change according to person.
Spiritual life is a constant struggle between ourselves and our internal /external world and these obstacles are itself are the resons for someone-to fall off -from-spiritual-life /journy.If he neglected his duty and by not following the spiritual guideline provided by scriptures.